Stator with improved pole shape for an eddy current braking system and eddy current braking system

Abstract

Stator (11, 12, 13) for an eddy current braking system, ECB, comprising: a yoke (11) in the form of a ring with a center M; a plurality of poles (12) distributed along a circular direction of the yoke (11) and fixed to the yoke (11); each pole (12) having an outer edge (121), an inner edge (122) facing the yoke center point M, and two pole flanks (123) connecting the outer edge (121) and inner edge (122), and a plurality of coils (13), each coil (13) being arranged around a corresponding pole (12), characterized in that the pole flanks (123) of two adjacent poles (12) are parallel to each other.

Description

The present invention relates to a stator for an eddy current brake system (ECB) and an eddy current brake system comprising such a stator and a drive unit having such an eddy current brake system.Prior ArtAn eddy current brake functions according to the principle of electromagnetic induction. When a conductor moves in a magnetic field, electric currents are induced in the conductor, which are referred to as eddy currents. These eddy currents generate their own magnetic fields which oppose the movement of the primary magnetic field responsible for their induction. This resistance generates a force that decelerates the moving conductor.The strength of the braking force in an eddy current brake is adjustable. By varying the strength of the magnetic field, typically by modulating the current in an electromagnet, the strength of the braking can be controlled. Permanent magnets whose magnetic field strength is constant can also be used.The term "axial" refers to the orientation of the stator components with respect to the axis of rotation of the system. In axial ECB designs, the magnetic flux in the air gap flows along the axis of rotation.Eddy current brakes have a stator with coils wound around poles and a rotor which moves in the magnetic field generated by the coils and in which the eddy currents are generated. The poles may be, for example, rectangular or trapezoidal. These poles have an outer edge, an inner edge and pole flanks which connect the outer edge and inner edge to each other. The outer edge and the inner edge of the poles are shaped as circle sections, with the center of the circle lying on the axis of rotation of the system.This results in the disadvantage that, due to the shape of the inner edge of the pole, automatic winding of the coils is difficult to achieve, if at all.In known eddy current brakes with an axial air gap, the poles and coils are frequently shaped in such a way that an extension of the pole flank intersects the axis of rotation and a right angle is thereby produced between the pole flank and the speed vector of the rotor. This results in a current in the rotor along a line which lies opposite the pole flank. The current is thus perpendicular to the direction of movement.This results in the disadvantage that the gap between the poles increases radially outwards. The gap is not filled with windings from the coils nor by poles. As a result, the installation space is not optimally utilized.It is the object of the invention to provide a stator in which the disadvantages from the prior art are reduced.Disclosure of the InventionThe present invention relates to a stator for an eddy current brake system and an eddy current brake system.According to the present invention, a stator comprising a yoke in the form of a ring having a center, a plurality of poles distributed along a circular direction of the yoke and fixed to the yoke, a plurality of coils, each coil being disposed around a corresponding pole, each pole having an outer edge, an inner edge facing the yoke center, and two pole flanks connecting the outer edge and the inner edge. Furthermore, the pole flanks of two adjacent poles are parallel to one another.The poles are trapezoidal, the trapezoidal shape being chosen such that the pole flanks of two adjacent poles are parallel to one another. This results in the advantage that the distance between the adjacent pole flanks is constant and the installation space can be better utilized, wherein the surface can be utilized either by the pole or by the winding. Studies by the applicant have shown that the resulting torque is greater in the configuration according to the invention of the pole flanks than in the pole flanks according to the prior art. Simulations and measurements by the applicant have shown that, with the same current through the coils, a greater torque M is achieved in a stator having the pole shape according to the invention as a function of the rotational speed n than in a stator having the pole shape according to the prior art, see also FIG.. 3Preferred refinements are the subject matter of the dependent claims.In a further development of the invention, the gap between two adjacent, parallel pole flanks has a rectangular shape. The windings of the coils of the respective pole run in the rectangular gap. The windings of the coils of the adjacent poles also extend substantially parallel to each other in the gap. The coils of the adjacent poles have a spacing of less than 2 mm, in particular in the range of less than 1.5 mm and / or greater than 0.5 mm, in particular of approximately 1 mm.In one embodiment of the invention, the pole flanks of all poles are parallel to their respective adjacent pole flank. As a result, the above-described advantageous technical effects are more pronounced.In addition to the parallel pole flanks, it is advantageous for the automated winding of the coils around the poles if the poles have rounded corners. The corners have, for example, a radius of 2 mm to 5 mm.Additionally or alternatively, it has proven advantageous for the automated winding if the inner edge of the poles has a convex shape. In other words, the inner edge of the pole bulges in the direction of the center point of the stator.The rounded corners of the poles and the convex inner edge of the poles each result in the fact that, during the automatic winding of the respective coils around the poles, the voltage on the coil wire can be kept easier and the automated winding is therefore only made possible. When both features are realized, they positively complement each other in the technical effect.The invention further relates to an eddy current brake system, ECB, having a stator according to the invention and a rotor.Furthermore, the invention also relates to a drive unit having an eddy current brake system according to the invention and an electric motor which is configured to drive at least one wheel of a vehicle, wherein the eddy current brake system and the electric motor have a common drive shaft.In an electric vehicle, the drive unit can be used as a central drive unit or as a single-wheel drive.The details of one or more embodiments are shown in the accompanying drawings and the following description. Further features are evident from the description and the drawings and from the claims.Brief Description of the DrawingsFIG. 1 is a 3D view of a yoke partially equipped with poles and coils according to an embodiment of the present invention in an approximate front direction. FIG. 2 is a 3D view of a yoke partially equipped with poles and coils according to a second embodiment of the present invention in an approximate front direction. FIG. 3 is a graph of torque in an eddy current brake system having a stator according to the prior art versus torque in an eddy current brake system having a stator according to the invention FIG. 4 is a schematic diagram of a drive unit.DETAILED DESCRIPTION OF THE INVENTIONHereinafter, the embodiments will now be described in detail with reference to the accompanying drawings. However, the disclosure may not be limited to the embodiment in which the concept of the disclosure is illustrated, and another embodiment included in the scope of the concept of another back disclosure, or the present disclosure may be easily proposed by adding, changing, brushing, and the like of another element.The terms used in this specification have been chosen to include current, widely used general terms. In certain cases, it may be a term that has been established by the applicant. In such cases, the meaning of the term is defined in the corresponding part of the detailed description. Thus, the terms used in the specification are not to be defined simply by their name, but to be defined based on the meaning of the terms and the general description of the present disclosure.Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is noted that the same or similar elements in the drawings are denoted by the same reference numerals.The axial design has advantages, one of which is the simplification of the overall construction of the brake system. The alignment provides for a uniform flux of the magnetic flux, so that the braking force is distributed uniformly over the braking surface. This leads to a reliable and uniform braking performance. This applies in particular when the eddy current brake is used as a central brake in a vehicle.An alternative design for the eddy current brake is the eddy current brake with a radial arrangement of stator and rotor with respect to one another. In the radial design of the eddy current brake, a uniform distribution of the magnetic flux over the circumference and thus a uniform distribution of the braking force also results.In contrast, a locally limited distribution of braking force results in the mechanical brake, since the brake caliper presses on the brake disc only at one point on the circumference.In contrast to electric machines which generate an alternating magnetic field, an eddy current brake generates a direct magnetic field by direct current in the stator. Therefore, the stator can be made of solid iron or steel instead of laminated electric sheets.Various materials may be used for the coils. For example, aluminum, advantageously with an anodized surface layer. Advantages include cost efficiency, high temperature resistance and light weight. Alternatively, copper can also be used, advantageously with a lacquer insulation. In this case, the advantages are the low resistance of copper and the fact that it is an established technology.For coils, flat ribbon wire or round wire can be used. The flat copper strip windings can advantageously be provided with an alternative insulation, for example a foil, instead of varnishing. For round wire windings that are more conventional, painted wires and enameling may use.FIG. 1 shows a 3D view of a stator 1 for an eddy current brake system 21 with a yoke 11 which is partially equipped with poles 12 and coils 13 fastened around the poles 12, approximately from the front. By front view is meant the side of the yoke 11 which, after assembly, faces the rotor of the ECB.The yoke 11 may be a hollowed disk or a ring having fixing holes at positions along its circular direction to place the poles 12 dispersedly. In advantageous embodiments, the positions of the poles 12 are distributed along the circular direction of the yoke 11 so that they can be placed on the yoke 11 so that the assembled yoke is rotationally symmetrical from the center of the ring that it forms (for example with a continuous distribution of the attachment positions of the poles in the circular direction). In this embodiment there are six positions for six poles 12 and their respective coils 13, In other embodiments there may be more or fewer poles depending on the diameter of the stator. The fastening holes can serve, for example, for screw or bolt connections for fastening the poles 12 to the yoke 11. Other types of fastening are also conceivable.In advantageous embodiments, the poles 12 have, as seen from the front, a substantially trapezoidal shape, the short side of the trapezoid being on the side of the centre M of the ring forming the yoke 11. This short side is the inner edge 122 of the pole 12, opposite its radially outer side is the outer edge 121 of the pole 12, the pole 12 being laterally bounded by its pole flanks 123. According to the invention, the mutually facing pole flanks 123 of two adjacent poles 12 are parallel to one another. This has the advantage that the area of the ring that can be occupied by the poles 12 and the coils 13 (as shown in FIG. 1 ) is increased, whereby the space provided in the eddy current brake system 21 can be optimally utilized.The poles 12 can be assembled with their respective coils 13 by winding directly one coil 13 around each pole 12. The poles 12 in this embodiment have rounded corners 124, thereby enabling and facilitating automated winding of the coils 13 around the poles 12.In advantageous embodiments, the thickness of the coil 12, viewed from the front, is substantially equal to half the distance between two adjacent poles 11, so that no space is lost in the circular direction around the yoke 11 once all the adjacent poles 12 are provided with their respective coils 13. For example, a possible distance D between adjacent coils 12 is less than 2 mm.The second embodiment of the invention in Fig. 2 differs from the first embodiment shown in Fig. 1 in that the inner edge 122 of the poles 12 have a convex shape. In Fig. 1, the inner edges 122 of the poles 12 have a concave shape. Otherwise, the two embodiments are the same.FIG. 3 is a graph showing a simulation for the torque. The torque M in Nm produced by the coils is plotted against the rotational speed n in 1 / min of the rotor. The coils have 1000 windings, with a current of 5A flowing per winding. The curve marked A is the resulting torque M in an eddy current brake system with a stator according to the prior art, in which two adjacent pole flanks enclose an angle. The curve marked B is the resulting torque M in an eddy current brake system with a stator according to the invention, in which two adjacent pole flanks are parallel to one another. It can be clearly seen that with increasing rotational speed n in an eddy current brake system with the stator according to the invention, the generated torque M is significantly higher than in an eddy current brake system from the prior art.FIG. 4 shows a drive unit 20. The drive unit 20 comprises an electric motor 23 and an eddy current brake system 21 according to the invention. The eddy current brake system 21 comprises the stator 1 according to the invention and a rotor which is connected in a rotationally fixed manner to a drive shaft 22. The stator 1 and the electric motor 23 are also seated on this drive shaft 22.

Claims

A stator (1) for an eddy current brake system, ECB, comprising: • a yoke (11) in the form of a ring having a centre M; • a plurality of poles (12) distributed along a circular direction of the yoke (11) and fixed to the yoke (11); wherein each pole (12) has an outer edge (121), an inner edge (122) facing the yoke centre M and two pole flanks (123) connecting the outer edge (121) and inner edge (122), and • a plurality of coils (13), wherein each coil (13) is arranged around a corresponding pole (12), characterized in that the pole flanks (123) of two adjacent poles (12) are parallel to each other.Stator (1) according to Claim 1, characterized in that, in a gap between two adjacent, parallel pole flanks (123), the windings of the coils (13) respectively belonging to the poles (12) are led along, and in that the coils (13) of the adjacent poles (12) have a spacing D of less than 2 mm.Stator (1) according to Claim 1 or 2, characterized in that the pole flanks (123) of all poles (12) are parallel to their adjacent pole flank (123).A stator (1) according to any preceding claim, characterized in that the poles (12) have rounded corners (124).The stator (1) according to claim 4, characterized in that the rounded corners (124) of the poles (12) have a radius of not less than 2 mm and / or not more than 5 mm.A stator (1) according to any one of the preceding claims, characterized in that the inner edge (122) of at least one pole (12) has a convex shape.An eddy current brake system (21), ECB, comprising: a stator (1) according to any one of claims 1 to 6, and a rotor.Drive unit (20) having an eddy current brake system (21) according to Claim 7 and an electric motor (23) which is configured to drive at least one wheel of a vehicle, characterized in that the eddy current brake system (21) and the electric motor (23) are seated on a common drive shaft (22).

Images