Pole head of optimized shape for a wound rotor of a rotary electric machine

Abstract

The invention relates to a wound rotor (1) with salient poles (2) comprising a main body made of magnetic material comprising a plurality of poles (2) arranged radially between a central part and a circumferential part of the rotor (1) so as to define an alternation of arms (8) each wound with an excitation coil (12) and slots (10). The arms (8) are each capped by a pole head that extends ortho-radially so as to protrude on either side of the arm (8). Each pole head has a base (16) connected to the arm (8) and an outer periphery having a convex surface. The convex surface of the pole head has a curved central region with a constant radius of curvature (R) and two narrower lateral regions (20a, 20b) located on either side of the central region.

Description

[0001] POLE HEAD WITH OPTIMIZED SHAPE FOR A WOUND ROTOR OF A ROTATING ELECTRIC MACHINE

[0002] The present invention relates to a rotor for a synchronous rotating electrical machine of the wound rotor type with salient poles, and in particular to an electrical machine of this type for applications as an electric traction motor in electric and hybrid motor vehicles.

[0003] Conventional wound rotor synchronous machines with salient poles comprise a rotor having a main body of magnetic material consisting of a pack of pre-cut laminations stacked parallel to the rotor's axis of rotation. The stacking of laminations then defines an alternation of arms and notches arranged radially between a central part and a circumferential part of the rotor.

[0004] The arms and slots extend axially along the rotor body, so as to define a plurality of alternating north and south poles, formed from a plurality of excitation coils wound around a respective radial arm between two consecutive slots. Each radial arm is then substantially aligned with a median radial axis of a corresponding pole. A stator surrounds the rotor with an air gap between the stator and the rotor.

[0005] In the field of electrical machines for the applications mentioned above, wound rotor synchronous machines have a high number of poles and a high content of harmonic components of voltage and electromagnetic torque. The harmonics of the electromagnetic torque can cause significant vibrations.

[0006] To mitigate these damaging effects impacting the operating quality of these electrical machines, it is necessary to reduce the harmonic components in order to reduce the influence of the electromagnetic coupling between the rotor and stator windings generated by these harmonic components.

[0007] The objective of the present invention is to propose a wound rotor electrical machine in which the shape of the rotor poles makes it possible to generate a significant mass torque while minimizing the torque harmonics in order to limit the vibrations that said harmonics can generate. Thus, the objective of the present invention is to obtain a good compromise between the performance in terms of torque generated with such an electrical machine and the limitation of the torque ripples generated by the rotation of the rotor within the electrical machine.

[0008] Another objective of the invention is to propose an electric machine that is more compact than those known from the state of the art.

[0009] Summary of the invention

[0010] The invention therefore relates to a wound rotor with salient poles comprising a main body made of magnetic material comprising a plurality of poles arranged radially between a central part and a circumferential part of the rotor so as to define an alternation of arms and notches, in which the arms project in a radial direction, the poles being formed from a plurality of excitation coils wound around the respective arms between two neighboring notches, the arms each being capped with a pole head extending orthoradially projecting on either side of the arm, said pole head comprising a base connected to said arm and an external periphery having a convex surface, the rotor being characterized in that the convex surface of the pole head has a curved central zone with a constant radius of curvature and two narrowed lateral zones located on either side of the central zone.According to a particular embodiment, the lateral zones of the convex surface of the pole head each have a shape in the form of a portion of an ellipse whose Cartesian coordinates x and y in a Cartesian reference system satisfy the following equations:. in which and in which: x_scale is a multiplier coefficient; y_scale is a multiplier coefficient;

[0011] De denotes the distance between an origin of the Cartesian reference frame and the center of the ellipse which gives its shape to the said lateral zones of the convex surface of the pole head;

[0012] 0 is a parameter that designates the polar angle; p is a parameter that designates the distance between the center of the ellipse and a point considered on the ellipse; a is a first variable that allows the parameter p to be varied; b is a second variable that allows the parameter p to be varied.

[0013] According to one embodiment, the first variable a is between 10 and 20, or even between 14.42 and 14.62, or even equal to 14.5 and the second variable b is between 20 and 30, or even between 25.44 and 25.74, or even equal to 25.56. According to one embodiment, the distance between the origin of the Cartesian reference frame and the center of the ellipse which defines the portion-elliptical shape of the lateral zones of the convex surface of the pole head is between 40 mm and 75 mm, or equal to 57.1 mm.

[0014] According to one embodiment, the constant radius of curvature which determines the curvature of the curved central zone is between 50 and 90 mm or equal to 77.15 mm.

[0015] According to one embodiment, each of the lateral zones is connected to the central zone by a first continuity fillet.

[0016] According to one embodiment, the first continuity fillet has a radius of curvature of between 1 and 60 mm, or even between 2.76 and 7.76 mm or equal to 4.76 mm.

[0017] According to one embodiment, the ends of the external periphery of the pole head are connected to lateral edges located at the base of the pole head by a second continuity fillet and the second continuity fillet has a radius of curvature of between 2.5 and 0.5 mm or equal to 1 mm.

[0018] According to one embodiment, the multiplier coefficients x_scale and y_scale are each between 0.8 and 1.2, or even between 1 and 1.012, or even equal to 1.

[0019] The invention also relates to an electrical machine with a wound rotor with salient poles which comprises such a rotor and a stator surrounding said rotor so as to define an air gap of variable dimension between the stator and the rotor. Presentation of the figures

[0020] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of different particular embodiments made without limitation in relation to the attached figures among which:

[0021] Figure 1 is a schematic detail view of an electrical machine comprising a salient pole rotor according to a preferred embodiment of the invention.

[0022] Figure 2 is another schematic detail view of the electric machine of Figure 1.

[0023] Figure 3 is a schematic detail view of a pole head of the salient pole rotor according to a preferred embodiment of the invention.

[0024] Figure 4 is a graph that represents the Cartesian coordinates of a set of points of the lateral areas of the convex surface of the pole head.

[0025] Figure 5 is a graph that represents the changes in the torque of different types of rotor as a function of the position of the rotor.

[0026] Detailed description

[0027] In Figure 1 is illustrated a portion of an electrical machine comprising a rotor 1 with salient poles 2 according to a preferred embodiment of the invention. This electrical machine therefore comprises a rotor 1 with salient poles 2 and a stator 3 surrounding said rotor 1 so as to define an air gap 4 between the stator 3 and the rotor 2.

[0028] The wound rotor 1 with salient poles 2 comprises a main body made of magnetic material. A plurality of poles 2 are arranged radially between a central portion of the main body and a circumferential portion of the rotor 1 so as to define an alternation of arms 8 and notches 10, as illustrated in FIG. 1. The arms 8 project in a radial direction relative to the main body of the rotor 1. The poles 2 are then formed from a plurality of excitation coils 12 wound around the respective arms 8 between two neighboring notches 10. Each arm 8 is capped with a pole head 14 extending orthoradially in projection on either side of said arm 8.

[0029] Each pole head 14 comprises on the one hand a base 16 connected to an arm 8 and on the other hand an external periphery having a convex surface 17. The convex surface 17 of the pole head 14 has a curved central zone 18 with a constant radius of curvature R and two narrowed lateral zones 20a, 20b which are located on either side of the central zone 18. At the level of the curved central zone 18, the constant radius of curvature R ensures an air gap 4 between the stator 3 and the rotor 1 with a constant distance.

[0030] In order to maximize the torque generated by the electrical machine, it is preferable to have a minimal air gap 4 between the pole heads 14 of the rotor 1 and the stator 3, in particular at the level of the curved central zone 18 of the convex surface 17. As an indication, the air gap 4 is for example between 0.5 mm and 1.5 mm.

[0031] According to a preferred embodiment, the constant radius of curvature R which determines on the one hand the curvature of the curved central zone 18 and on the other hand the distance of the air gap 4 between the stator 3 and the curved central zone 18 of the convex surface 17 of the pole heads 14 of the rotor 1, is between 50 and 90 mm. According to a preferred embodiment, the constant radius of curvature R is equal to 77.15 mm.

[0032] For the pole head 14, each of the lateral zones 20a, 20b is connected to the central zone 18 by a first continuity fillet r1, as illustrated in FIGS. 2 and 3. According to one embodiment, the first continuity fillet r1 has a radius of curvature between 1 and In a preferred embodiment, the first continuity fillet r1 is between 2.76 and 7.76 mm. According to a particular example, the first continuity fillet r1 which connects each of the lateral zones 20a, 20b to the central zone 18 is equal to 4.76 mm. Such a first continuity fillet r1 makes it possible to ensure a smooth transition between each of the lateral zones 20a, 20b to the central zone 18 while simplifying the manufacture of the pole head 14.

[0033] The two lateral zones 20a, 20b located on either side of the central zone 18 are narrowed in the sense that the air gap 4 which is constant between the rotor 1 and the stator 3 at the level of the curved central zone 18 of the pole head 14 is no longer constant at the level of the two lateral zones 20a, 20b. The air gap 4 has a flared shape at the level of the two lateral zones 20a, 20b; this air gap 4 thus has a gradually larger gap between the convex surface 17 of the pole head 14 and the stator 3. In other words, the air gap 4 between the convex surface 17 of the pole heads 14 and the stator 3 is not constant, but has variable dimensions.

[0034] According to a preferred embodiment, the lateral zones 20a, 20b of the convex surface 17 of the pole head 14 each have a portion of an ellipse shape. This ellipse is based on a specific geometric shape defined from a geometry commonly called “Cassini oval”.

[0035] The points located on these lateral zones 20a, 20b have Cartesian coordinates which verify the following equations:

[0036] [Math 1]

[0037] [Math 2]

[0038] [Math 3]

[0039] In these equations, the parameter De designates the distance between the origin of the Cartesian reference frame used and the center of the ellipse which gives its shape to said lateral zones 20a, 20b of the convex surface 17 of the pole head 14. The parameter 0 designates the polar angle and p is a parameter which designates the distance between the center of the ellipse and the point considered on the ellipse for which its x and y coordinates are calculated.

[0040] The origin of the Cartesian reference frame is located at the base of the arm 8. According to one embodiment, the distance De between the origin of the Cartesian reference frame and the center of the ellipse which defines the portion-elliptical shape of the lateral zones 20a, 20b of the convex surface 17 of the pole head 14 is between 40 mm and 75 mm. According to a preferred example, this distance De is equal to 57.1 mm.

[0041] A first X axis of the Cartesian coordinate system extends orthoradially on either side of the radial arm 8. A second Y axis of the Cartesian coordinate system extends perpendicular to the X axis. The first X axis and the second Y axis are illustrated in Figures 3 and 4.

[0042] In this reference frame, the Y axis forms an axis of symmetry for the curved central zone 18 and for the lateral zones 20a, 20b located on either side of said curved central zone 18. In other words, the Y axis passes through the middle of the curved central zone 18 and forms an axis of symmetry for the lateral zones 20a, 20b arranged symmetrically on either side of the Y axis. In this same reference frame, the angle 0 varies between 45.585° and 62.5° for a first lateral zone 20a. The coordinates for x then vary between 22.38 and 14.00 while the coordinates for y then vary between 71.38 and 75.87. As illustrated in Figure 4, the x and y coordinates of the points of the convex surface 17 in the first lateral region 20a are located above the Y axis.

[0043] Still in this same frame of reference, the angle 6 varies between 117.5° and 134.415° for a second lateral zone 20b. The coordinates for x then vary between -14.00 and -22.38 while the coordinates for y then vary between 75.87 and 71.38. As illustrated in Figure 4, the x and y coordinates of the points of the convex surface 17 in the second lateral zone 20b are located below the Y axis.

[0044] In the Math 3 equation which defines the parameter p, the variables a and b have an influence on the shape of the ellipse, in particular they allow the rate of curvature of the ellipse to be modified and consequently the parameter p to be varied.

[0045] According to one embodiment, the first variable a is between 10 and 20, or even between 14.42 and 14.62. According to a preferred example, the first variable a is equal to 14.5.

[0046] Similarly, the second variable b is between 20 and 30, or even between 25.44 and 25.74. In a preferred example, the second variable b is equal to 25.56.

[0047] In the equations Math 2 and Math 3, x_scale is a multiplier coefficient and y_scale is also a multiplier coefficient. In one embodiment, the multiplier coefficients x_scale and y_scale are each between 0.8 and 1.2, or even between 1 and 1.012. In a preferred example, the multiplier coefficients x_scale and y_scale are both equal to 1. These multiplier coefficients have an influence on the size of the ellipse which determines the shape of the lateral zones 20a and 20b of the convex surface 17 of the pole head 14.

[0048] Furthermore, the ends of the outer periphery of the pole head 14 are connected to lateral edges located at the base 16 of the pole head 14 by a second continuity fillet r2, as illustrated in FIGS. 2 and 3. According to one embodiment, the second continuity fillet r2 has a radius of curvature of between 2.5 and 0.5 mm. In a preferred embodiment, the second continuity fillet r2 has a radius of curvature equal to 1 mm. Such a second continuity fillet r2 makes it possible to ensure a smooth transition between the ends of the outer periphery of the pole head 14 and the lateral edges located at the base of the pole head 14 while simplifying the manufacture of said pole head 14.

[0049] An electrical machine with a wound rotor 1 equipped with a rotor 1 which has poles 2 with a specific pole head 14 according to the invention makes it possible in operation to maximize the average torque obtained while making it possible to limit torque ripples and induction harmonics in the air gap.

[0050] Such an electrical machine with a wound rotor 1 equipped with a rotor 1 which has poles 2 with a specific pole head 14 according to the invention makes it possible to maximize the torque generated while minimizing the vibrations caused by the rotation of the rotor 1. In other words, equipping an electrical machine with a wound rotor 1 with a rotor 1 according to the invention makes it possible to limit the torque ripples of the electrical machine, so as to keep these torque ripples at a reasonable level. This is illustrated in the graph of Figure 5.In this figure 5, the torque obtained with a rotor comprising poles with smooth pole heads, that is to say pole heads with a convex surface defined by a constant radius of curvature so as to keep a constant air gap between the stator and the rotor of the machine, shows much more pronounced peaks than the torque obtained with a rotor comprising poles with pole heads having a specific shape according to the invention.

[0051] In other words, the particular shape of the lateral zones 20a and 20b at the ends of the pole heads 14 makes it possible to reduce the harmonic components so as to reduce the influence of the electromagnetic coupling between the windings of the rotor 1 and the stator 3 generated by these harmonic components. It is thus possible to obtain a good compromise between the average torque generated with such an electrical machine and the limitation of torque ripples.

Claims

CLAIMS 1 . Wound rotor (1) with salient poles (2) comprising a main body made of magnetic material comprising a plurality of poles (2) arranged radially between a central part and a circumferential part of the rotor (1) so as to define an alternation of arms (8) and notches (10), in which the arms (8) project in a radial direction, the poles (2) being formed from a plurality of excitation coils (12) wound around the respective arms (8) between two neighboring notches (10), the arms (8) each being capped with a pole head (14) extending orthoradially projecting on either side of the arm (8), said pole head (14) comprising a base (16) connected to said arm (8) and an external periphery having a convex surface (17), the rotor (1) being characterized in that the convex surface (17) of the pole head pole (14) has a curved central zone (18) with a constant radius of curvature (R) and two lateral zones (20a,20b) narrowed located on either side of the central zone (18)., 2. Rotor according to the preceding claim, characterized in that the lateral zones (20a, 20b) of the convex surface (17) of the pole head (14) each have a shape in the form of a portion of an ellipse whose Cartesian coordinates (x, y) in a Cartesian reference system satisfy the following equations: in which and in which: x_scale is a multiplier coefficient; y_scale is a multiplier coefficient; De denotes the distance between an origin of the Cartesian reference frame and the center of the ellipse which gives its shape to said lateral zones (20a, 20b) of the convex surface (17) of the pole head (14); 6 is a parameter that designates the polar angle; p is a parameter that designates the distance between the center of the ellipse and a point considered on the ellipse; a is a first variable that allows the parameter p to be varied; b is a second variable that allows the parameter p to be varied.

3. Rotor according to the preceding claim, characterized in that the first variable a is between 10 and 20, or even between 14.42 and 14.62, or even equal to 14.5 and in that the second variable b is between 20 and 30, or even between 25.44 and 25.74, or even equal to 25.

56.

4. Rotor according to one of claims 2 to 3, characterized in that the distance (De) between the origin of the Cartesian reference and the center of the ellipse which defines the shape in portion of ellipse of the lateral zones (20a, 20b) of the convex surface (17) of the pole head (14) is between 40 mm and 75 mm, or equal to 57.1 mm.

5. Rotor according to one of claims 2 to 4, characterized in that the constant radius of curvature (R) which determines the curvature of the curved central zone (18) is between 50 and 90 mm or equal to 77.15 mm.

6. Rotor according to one of the preceding claims, characterized in that each of the lateral zones is connected to the central zone (18) by a first continuity fillet (r1).

7. Rotor according to the preceding claim, characterized in that the first continuity fillet (r1) has a radius of curvature of between 1 and 60 mm, or even between 2.76 and 7.76 mm or equal to 4.76 mm.

8. Rotor according to one of the preceding claims, characterized in that the ends of the external periphery of the pole head (14) are connected to lateral edges located at the base (16) of the pole head (14) by a second continuity fillet (r2) and in that the second continuity fillet (r2) has a radius of curvature between 2.5 and 0.5 mm or equal to 1 mm.

9. Rotor according to one of the preceding claims, characterized in that the multiplying coefficients x_scale and y_scale are each between 0.8 and 1.2, or even between 1 and 1.012, or even equal to 1.

10. Synchronous electric machine with wound rotor (1) with salient poles (2), characterized in that it comprises a rotor (1) according to any one of the preceding claims and a stator (3) surrounding said rotor (1) so as to define an air gap (4) of variable dimension between the stator (3) and the rotor (1).

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