Rotor of electric motor and electric motor having such rotor

Abstract

The invention relates to a rotor (10) for an electric motor (12) and an electric motor (12), the rotor having a base body (20) which extends concentrically around an axial rotor shaft (14), wherein the base body (20) consists of individual axially stacked plate stacks (32), wherein a magnet recess (18) is formed in a radially outer region (23) of the plate stack, into which a permanent magnet (16) engages, and a pole cap (40) having an outer contour (11) is formed radially outside the magnet recess (16), wherein an axial weld (55) is formed in the pole cap (40) which connects at least two uppermost plate stacks (32) to one another in an axial direction (8) in a material-locking manner.

Description

Technical Field

[0001] The invention relates to a rotor of an electric machine and an electric machine having such a rotor. Background Art

[0002] DE 10 2007 005 032 A1 discloses an electric motor having a rotor with a laminated core, wherein magnets are arranged in recesses within the laminated core. The magnets are constructed to be longer in the circumferential direction than in the radial direction and are held in the recesses by means of elastic webs. Radially outside the magnets, rotor poles are arranged which are axially stacked from individual laminations. These laminations are axially connected to one another. However, in certain applications, undesirable axial movements of the laminations relative to one another may occur in the radially outer region, which is associated with disruptive noise generation or, in extreme cases, fatigue / fracture of the pole caps. This disadvantage is intended to be eliminated by the solution according to the invention. Summary of the invention

[0003] In contrast, the rotor and the electric machine according to the invention with the features of the independent claims have the advantage that the plate stack is reliably connected to one another even in the radially outer region by welding in the axial direction through the pole cap. This prevents the plate stack from vibrating relative to one another in the axial direction during operation and thus causing rattling noises. Contrary to the common view in the art, the axial welding radially inside the pole cap with a high magnetic flux can simultaneously reduce the rotor's holding torque. Such a rotor is therefore also suitable for applications with high holding torque requirements, such as, for example, for servo steering.

[0004] By means of the measures listed in the dependent claims, advantageous extensions and improvements of the embodiments given in the independent claims can be achieved. It is therefore particularly advantageous if the axial weld is constructed in the middle region of the pole cap with respect to its circumferential direction. By arranging the axial weld in the center, the pole caps are optimally connected to each other in the axial direction in order to suppress axial vibrations of the plate stack. At the same time, the middle circumferential region of the pole cap is the region with the maximum magnetic flux density. Contrary to the common expertise to date, it has been shown that the stopping torque can be positively influenced by changing the material in the pole cap by welding in the region of the maximum magnetic flux. By arranging the axial weld in the region of the maximum magnetic flux, the magnetic flux is constructed more uniformly with respect to the circumferential direction of the rotor.

[0005] This effect is particularly advantageous in magnet recesses that are designed to be completely closed across their entire circumference transversely to the rotor axis. In this case, the pole caps are located radially outside the magnet recesses and are connected to the radial inner region of the plate stack on both of their tangential sides via radial retaining webs. In this embodiment, the extension of the pole caps in the circumferential direction is significantly greater than their extension in the radial direction. This also applies to permanent magnets that are pressed into the magnet recesses.

[0006] In this arrangement, in which the approximately square permanent magnets have a greater extent in the tangential direction than in the radial direction, the magnetic field lines extend from the permanent magnets in the radial direction through the pole caps to the outer contour of the rotor. In this case, the permanent magnets have a magnetization in the radial direction, so that pole caps with north poles alternate with pole caps with south poles in the circumferential direction.

[0007] In principle, it is also conceivable that in a permanent magnet storage assembly the pole segments between the tangentially magnetized permanent magnets are arranged in the radially outer region by means of such axial welding in order to axially fix the plate stack to one another in the radially outer region.

[0008] It is particularly advantageous if the individual plate stacks each have insulating surfaces which abut against one another in the axial direction. Eddy currents within the rotor are thereby reliably suppressed. Such an insulating coating can be achieved, for example, by heat treatment of the individual plate stacks or by means of a carbon-containing coating, such as, for example, a C3 or C5 coating. In the region of the axial weld, the pole caps are connected to one another in an axial direction by a material fit, so that the insulation is also destroyed in this region and the plate stacks are therefore in electrical contact with one another in the axial direction along the weld bulge.

[0009] The axial weld is particularly advantageously implemented by means of laser welding, wherein the laser beam passes completely through the first plate stack from the axial end face of the rotor cover in the axial direction and penetrates axially all the way to the second, third, fourth or fifth plate stack. This results in a weld point which is designed as an axial weld bulge in the axial direction and which is preferably arranged radially inside the outer contour of the rotor.

[0010] It is particularly advantageous if the axial weld is arranged within the pole cap in the vicinity of the permanent magnet. The holding torque is particularly advantageously influenced if the center point of the axial weld is arranged between 20% and 45% of the radial height of the pole cap in the radially inner region of the radial height. Surprisingly, it has been found that the holding torque can be significantly reduced by arranging the center point of the axial weld closer to the permanent magnet. However, the center point of the axial weld cannot be arranged arbitrarily close to the permanent magnet so as not to influence it so strongly during the welding process.

[0011] The laser weld has, for example, a circular cross section on the axial end face of the pole cap, which is larger than the cross section in the plate stack located below. Thus, the axial weld has a tapered cone in the axial direction, which preferably has a circular cross section.

[0012] Depending on the size of the rotor, the diameter of the axial weld on the axial end side of the pole cap is, for example, 0.8 mm to 1.8 mm. The diameter of the axial weld decreases with its axial depth, so that, for example, its diameter is only 0.1 to 0.5 mm in the second or third plate stack.

[0013] In order to influence the holding torque of the rotor in a targeted manner, the outer contour of the individual pole caps has an approximately sinusoidal shape or a so-called Richter contour. As a result, the circumference of the rotor deviates from a precise circle, so that the radius of the rotor is smaller at the edge region of the circumference of the permanent magnets than in the central circumferential region of the permanent magnets.

[0014] For a mechanically stable embodiment of the rotor, exactly one axial weld is formed on each pole cap, wherein the axial weld is preferably formed on two opposite axial end faces of the pole cap. This prevents the plate stacks from axially striking one another in each individual pole cap. The axial weld extends axially through a plurality of plate stacks.

[0015] The extension of the permanent magnet in the axial direction is preferably greater than the extension in the tangential direction and in the radial direction. To install the permanent magnet, the permanent magnet is simply pressed axially into the magnet recess, wherein the permanent magnet is pressed radially outward against the pole cap via spring tabs formed on the laminated core. Rare earth magnets, in particular NdFeB, are preferably used as permanent magnets.

[0016] Such a rotor according to the invention is preferably arranged within a stator, which is part of an electric machine. The electric machine is preferably designed as an electrically commutated electric motor, wherein the stator has an electronically commutated winding which sets the rotor in motion with the permanent magnets. Such an EC motor is preferably used as a steering assist drive in a motor vehicle, but can also be used for other control drives of components in a motor vehicle or for rotary drives for rotation. Such an electric machine with a low braking torque can of course also be used for applications outside of motor vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the following description, preferred embodiments of the present invention are described in detail with reference to the accompanying drawings, in which corresponding elements are provided with identical reference numerals. It is shown in the drawings:

[0018] Figure 1 A view showing a rotor according to the invention of an electric machine,

[0019] Figure 2 A detail view showing an axial top view of the rotor, and

[0020] Figure 3 Another embodiment of a rotor is shown in side view. DETAILED DESCRIPTION

[0021] exist Figure 1 1 shows a rotor 10, such as is used, for example, in an electric machine 12. The rotor 10 has a rotor shaft 14, on which a base body 20 is arranged concentrically therewith. The base body 20 is, for example, pressed onto the rotor shaft 14. The base body 20 consists of individual plate stacks 32, which are stacked axially one above the other in the axial direction 8. The individual plate stacks 32 are, for example, stamped out of electrical steel sheets and are pressed together with respect to the axial direction 8, preferably by means of stamping stacking.

[0022] For this purpose, preferably the following caulking points 80 are formed radially inside the permanent magnets 16, which connect all the plate laminations 32 to each other. In the radial inner region 22, the base body 20 has a relatively large recess 24, so that the radial outer region 23 is connected to the hub 28 of the base body 20 only by relatively thin radial webs 26. As a result, the rotor size and the moment of inertia of the rotor are mainly reduced. In the radial outer region 23, the following magnet recess 18 is hollowed out in the base body 20, into which the permanent magnet 16 is axially engaged. In this embodiment, the permanent magnet 16 has a roughly rectangular cross section, the extension 34 of the rectangular cross section in the circumferential direction 9 is greater than the extension 35 of the permanent magnet 16 in the radial direction 7. The magnet recess 18 has a closed circumference, so that the permanent magnet 16 is completely arranged inside the circumferential surface of the rotor 10. Radially outside the magnet recesses 18, a pole cap 40 is formed, through which the magnetic flux is transferred from the permanent magnets 16 to the outer contour 11 of the pole cap 40. The pole cap 40 cooperates, for example, with a stator 42, which is arranged radially outside the rotor 10. The stator 42 has, for example, electronically commutated stator coils 43, which interact magnetically with the pole cap 40. Between the magnet recesses 18, retaining webs 19 are formed in the circumferential direction 9, which are part of the circumference of the magnet recesses 18. The permanent magnets 16 preferably rest on the retaining webs 19 in the circumferential direction 9. The retaining webs 19 transition into the pole cap 40 in the circumferential direction 9, so that the permanent magnets 16 are retained in the completely closed magnet recesses 18 toward the rotor shaft 14. An axial welded connection 55 is formed on the pole cap 40, which extends axially through at least two plate stacks 32 in order to connect them to one another in a material-locked manner. The axial welded connection 55 preferably does not extend over the entire axial length of the rotor 10, but rather only extends over the first two to five plate stacks 32, starting from the end sides 56, 57 of the rotor 10. According to the invention, the axial welded connection 55 is formed by means of laser welding, wherein a laser beam penetrates axially into the end side 56 of the rotor 10 and completely welds one or more plate stacks 32 to one another axially. In this case, the weld camber 58 is designed as a weld seam, which extends axially through the plate stack 32. Figure 1 Only the end face 56 of the rotor 10 with the axial welded connection 55 can be seen in FIG. However, preferably, an axial welded connection 55 is also formed on the opposite end face 57 on the pole cap 40 . Figure 1 In each pole cap 40 , exactly one axial welded connection 55 is formed over the entire circumference, in each case on the end faces 56 , 57 . This prevents the laminated core 32 from being able to move axially relative to one another on the outer contour 11 during operation of the electric machine 12 .

[0023] exist Figure 2A further exemplary embodiment of a rotor 10 according to the invention is shown in FIG. 1 as a detailed view of a section. The permanent magnets 16 engage in the magnet recesses 18 and are radially clamped in the magnet recesses 18 by means of clamping plates 38 .

[0024] For example, clamping plates 38 are formed here on the circumference of the magnet recesses 18, which clamp the permanent magnets 16 in the corresponding magnet recesses 18. In order to make the clamping plates 38 elastic, they are, for example, only punched out in every two or every n laminations, so that free spaces are formed between the clamping plates 38 in the axial direction 8. The permanent magnets 16 rest on the retaining tabs 19 on both sides in the circumferential direction 9. Formings 60 are respectively left open in the magnet recesses 18 in the circumferential direction 9 in order to reduce magnetic leakage losses. Figure 2 , it can be seen that the outer contour 11 of the pole cap 40 deviates from the circular shape 62. For example, the pole cap 40 has a sinusoidal contour 64 or a so-called straightener contour, by which the locking torque of the rotor 10 can be influenced accordingly. The axial welded connection 55 is arranged approximately centrally with respect to the extension of the pole cap 40 in the circumferential direction 9 at an axial side face 66 of the pole cap 40. The pole cap 40 has a radial height H, which extends radially from the magnet recess 18 to the outer contour 11 of the pole cap 40. The radial height H is configured to be maximum with respect to the circumferential direction 9 in the middle region. The axial welded connection has a center point 54, which is arranged in the range between 20% and 50% of the radial height H starting from the magnet recess 18. In order to have a positive influence on the locking torque, the center point 54 of the axial weld 55 is located in the range between 25% and 40% of the radial height H starting from the magnet recess 18. The cross section 53 of the laser weld 55 is preferably circular, but can also have a shape different from this. Since the center point 54 of the axial welded connection 55 is arranged radially within the radial height H of the pole cap 40 , the outer contour 11 of the pole cap 40 has no welds in this region.

[0025] In an alternative embodiment (not shown), more than one axial weld 55 can also be arranged within a pole cap 40 and / or the center point 54 of the weld connection 55 can also be arranged eccentrically with respect to the circumferential direction 9 .

[0026] Another embodiment of the rotor 10 according to the invention is Figure 3 The welding portion 55 is not visible on the outer contour 11 of the pole cap 40 . The axial welding portion 55 is arranged radially inside the pole cap 40 , so that the cross section 55 of the axial welding portion 55 does not intersect the outer contour 11 .

[0027] The axial weld 55 is shown here in the form of a dashed line as a weld bulge 58, the cross section 53 of which decreases from the axial end side 56 of the rotor 10 in the axial direction 8 from the plate stack 32 to the plate stack 32. For example, the diameter 52 of the approximately circular cross section 53 of the laser weld 55 on the axial end side 66 of the pole cap 40 of the first plate stack 31 is 0.7 mm to 2.0 mm. In the second plate stack 33, the diameter is already smaller, and in the third plate stack 36, the diameter 51 is, for example, only between 0.1 and 0.5 mm. The weld bulge 58 is Figure 3 55. However, alternatively, the welding arch 58 can also extend to the fourth or fifth plate stack 32. The welding arch 58 is conical in the side view shown, wherein an arched welding point 70 can be constructed on the end side 66 of the pole cap 40. In this embodiment, these individual plate stacks 32 have an insulating coating 72, so that eddy currents in the axial direction 8 are suppressed. The coating 72 can be constructed as a carbon-containing covering, which contains C3 or C5, for example. In the area of ​​the axial welding arch 58, the insulating coating 72 is melted, so that in the area of ​​the axial weld 55, the individual plate stacks 32 are electrically conductively connected to each other in the axial direction 8. The typical thickness 74 of these plate stacks 32 in the axial direction 8 is, for example, about 0.5 mm.

[0028] It should be noted that, with respect to the embodiments shown in the drawings and in the description, various combinations of individual features are possible. Thus, for example, the specific construction, arrangement and number of permanent magnets 16 with corresponding pole caps 40 can be varied. The specific position and construction of the axial weld 55 in the pole cap 40 can also be adapted to the requirements and manufacturing possibilities of the motor 12. By means of a specific design of the outer contour 11 of the pole cap 40, the desired holding torque of the motor 12 can be designed in combination with the arrangement of the axial weld camber 58. The present invention is particularly suitable for the rotational drive of components or the adjustment of components in motor vehicles, but can also be used for other applications, such as the drive of bicycles or power wheels. The motor 12 is preferably configured as a synchronous motor, which can be used as a drive device for different applications, in particular as a steering assistance motor for a servo steering device.

Claims

1. A rotor (10) for an electric machine (12), comprising a base body (20) which extends concentrically around an axial rotor shaft (14), wherein: The base body (20) consists of a single axially stacked lamination stack (32), a magnet recess (18) being formed in a radially outer region (23) of the lamination stack, into which a permanent magnet (16) engages, and a pole cap (40) having an outer contour (11) being formed radially outside the magnet recess (18). Characterized in that an axial weld (55) is formed in the pole cap (40), which connects at least the two uppermost plate stacks (32) to one another in an integrally bonded manner in the axial direction (8), The axial weld (55) is arranged centrally in the pole cap (40) with respect to a circumferential direction (9) of the rotor (10) and radially within the outer contour (11).

2. The rotor (10) according to claim 1, characterized in that The magnet recess (18) is designed to be completely closed, and the pole cap (40) is designed to be larger in the circumferential direction (9) than in the radial direction (7).

3. The rotor (10) according to claim 1, characterized in that The permanent magnets (16) are magnetized in a radial direction (7) such that magnetic field lines (50) of the permanent magnets extend radially outward through the pole cap (40) to the outer contour (11).

4. The rotor (10) according to claim 1, characterized in that The size of the permanent magnet (16) in the circumferential direction (9) is greater than the size in the radial direction (7).

5. The rotor (10) according to claim 1, characterized in that The laminated core (32) has an insulating layer (72) which electrically insulates the laminated core (32) from one another in an axial direction (8), the insulating layer connecting two axially adjacent laminated cores (32) to one another in an electrically conductive manner locally at the axial weld (55).

6. The rotor (10) according to claim 1, characterized in that The axial weld (55) is designed as a laser welding bend (58) which, starting from the axial end face (56) of the uppermost laminated core (32), axially projects at least as far as the second or third laminated core (32).

7. The rotor (10) according to claim 1, characterized in that The pole cap (40) has a radial height (H) from the magnet recess (18) to its outer contour (11), and the center point (54) of the axial weld (55) is arranged within the inner half (H / 2) of the radial height (H).

8. The rotor (10) according to claim 1, characterized in that The pole cap (40) has a radial height (H) from the magnet recess (18) to its outer contour (11), and the center point (54) of the axial weld (55) is arranged within an inner third of the radial height (H).

9. The rotor (10) according to claim 1, characterized in that The cross section (53) of the axial weld (55) is circular, and the diameter (52) of the cross section (53) decreases starting from the outer axial end side (56) of the uppermost plate core (32) with the axial depth (59) of the axial weld (55).

10. The rotor (10) according to claim 1, characterized in that The diameter (52) of the cross section (53) of the axial weld (55) is 1.0 to 2.0 mm at the outer axial end side (56) of the uppermost plate core (32) and 0.1 to 0.4 mm in the third plate core (32).

11. The rotor (10) according to claim 1, characterized in that The circumferential profile of the rotor (10) deviates from a precise circular shape (13), and the individual pole caps (40) have a sinusoidal or orthometric profile (64) or other spline profile.

12. The rotor (10) according to claim 1, characterized in that On both axial end sides (56, 57) of the rotor (10), exactly one axial weld (55) is arranged in each pole cap (40) with respect to the circumferential direction (9).

13. The rotor (10) according to claim 1, characterized in that The permanent magnet (16) is pressed radially outwardly against the pole cap (40) within the magnet recess (18) by means of clamping webs (38) formed on the laminated core (32).

14. An electric machine (12), wherein: A rotor (10) according to any of the preceding claims 1 to 13 is arranged radially inside a stator (42) which has an electronically commutated electrical winding (43).

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