Rotor and hydraulic pump

Abstract

The invention relates to a rotor (16) for an electric motor, having a motor shaft (18), a support (20), which is connected to the motor shaft (18) for conjoint rotation therewith, and a stack of rotor laminations (10), which are arranged on the support (20) and carry a plurality of permanent magnets (12). The rotor laminations (10) have a radial thickness (14) which changes periodically when viewed in the circumferential direction and which varies between a minimum value (30) and a maximum value (32), wherein the maximum value (32) lies on a radius which lies between two permanent magnets (12) that are adjacent in the circumferential direction, and the minimum value (30) lies on a radius which passes through the centre of a permanent magnet (12). The support (20) has a constant inside diameter. The invention also relates to a hydraulic pump having a rotor (16).

Description

[0001] Rotor and hydraulic pump

[0002] The invention relates to a rotor for an electric motor. The invention also relates to a hydraulic pump having a corresponding rotor.

[0003] There are numerous areas of application for electric motors in which only very little installation space is available. Therefore, various shapes of rotor have been developed that are adapted specifically to the available installation space and allow a very compact motor design. For example, cup-shaped rotors optimized to the installation space are often used in hydraulic pumps.

[0004] However, optimizing the installation space often also has effects on the efficiency of the motor, especially since the geometric boundary conditions require a departure from ideal shapes and / or spacings of magnets, lamination stacks and / or other rotor elements.

[0005] It is therefore the object of the invention to provide a system which is optimized both in respect of installation space and also of efficiency.

[0006] The object is achieved according to the invention by a rotor for an electric motor, having a motor shaft, a support, which is connected to the motor shaft for conjoint rotation therewith, and a stack of rotor laminations, which are arranged on the support and carry a plurality of permanent magnets. In this case, the rotor laminations have a radial thickness which changes periodically when viewed in the circumferential direction and which varies between a minimum value and a maximum value. The maximum value lies on a radius which lies between two permanent magnets that are adjacent in the circumferential direction, and the minimum value lies on a radius which passes through the centre of a permanent magnet. The support has a constant inside diameter.

[0007] The invention is based on the insight that more ferromagnetic lamination material can be introduced into the rotor by rotor laminations that have a radial thickness which varies periodically in the circumferential direction than in the case of conventional rotors. In this case, the additional lamination material is arranged selectively between two adjacent permanent magnets and thus very close to the magnetic poles (that is to say in regions with a high magnetic flux density). As a result, higher magnetic saturation flux densities can be achieved, and the efficiency of the motor is improved.

[0008] In the case of cup-shaped rotors, there is no need to change either the internal or the external geometry of the rotor in order to achieve this. For example, the additional space for ferromagnetic lamination material can be created by a special configuration of the support.

[0009] It has been found that rotors according to the invention have a high mechanical stability, despite the variation in the thickness of the laminations in the circumferential direction and the possibly adapted geometry of the support.

[0010] Moreover, only slight drag losses occur during the operation of electric motors with a rotor according to the invention on account of the constant inside diameter.

[0011] In one variant embodiment of the rotor according to the invention, the wall thickness of the support in the regions in which the rotor laminations have their maximum thickness is approximately half the wall thickness of the support in the regions in which the rotor laminations have their minimum thickness. In other words, the wall thickness of the support thus varies over the circumference between 52.4% and 100% of the maximum wall thickness. As a result, a particularly large amount of additional space can be created for ferromagnetic lamination material. It has been found that this configuration offers a particularly advantageous compromise between efficiency and mechanical stability.

[0012] Provision can furthermore be made for the outer contour of the support to change between concave and convex portions when viewed in cross section. By this means too, additional installation space can be created for additional lamination material. Moreover, it is possible in this way to adapt the shape of the support and of the rotor laminations arranged thereon specifically to the magnetic field profile, and this has a positive effect on the drive properties of the electric motor.

[0013] The support can consist of a plastic, for example. This allows rapid and low- cost manufacture adapted specifically to the geometry of the laminations. In particular, the support can be a plastic component which is moulded onto the rotor laminations and / or which is formed by moulding or overmoulding onto the rotor laminations.

[0014] In a preferred embodiment, the rotor laminations have a constant outer radius. In other words, the periodically changing radial thickness of the rotor laminations is not achieved by variation of the outer radius over the circumference but by variation of the inner radius. There is therefore no need to interfere with the functionally optimized round external geometry of the rotor.

[0015] The object is furthermore achieved by a hydraulic pump having a stator, a rotor according to the invention, and a pump module, wherein the pump module has a pump housing with a bearing portion in which the motor shaft is mounted.

[0016] The advantages which have already been discussed in relation to the rotor obviously also apply to the hydraulic pump.

[0017] In one variant embodiment of the hydraulic pump, the bearing portion and the support overlap in the axial direction. In particular, the rotor can be of cup-shaped configuration, wherein the bearing portion projects into the interior of the cup. This nested construction allows rigid or low-vibration and, at the same time, spacesaving mounting of the rotor.

[0018] In this context, provision can be made, in particular, for the bearing portion to extend into the support over more than half of the axial length of the latter. As a result, particularly close integration of the two components is achieved, and a very compact pump design is made possible.

[0019] It is also conceivable for the bearing portion to be provided on the outside with ribs which extend in the axial direction. The ribs reinforce the bearing portion. They improve its mechanical stability and increase the rigidity of the mounting.

[0020] In a preferred variant embodiment, a gap is provided between the ribs and the inside of the support. In particular, the gap can have a width which corresponds at least to the height of the ribs (i.e. to the extent of the ribs in the radial direction). This simplifies the assembly of the rotor and of the pump housing. In addition, the minimum gap size provided enables drag losses during the operation of the hydraulic pump to be kept low. Further features and advantages of the invention will emerge from the following description and from the appended drawings, to which reference is made in the following. In the drawings:

[0021] Figure 1 shows a schematic illustration of a conventional rotor lamination with inserted permanent magnets and the profile of the magnetic field lines;

[0022] Figure 2 shows a cup-shaped rotor known from the prior art;

[0023] Figure 3 shows a three-dimensional view of an embodiment of a rotor according to the invention;

[0024] Figure 4 shows a cross-sectional view of the rotor from Figure 2; and

[0025] Figure 5 shows a detail of a hydraulic pump according to the invention, comprising the rotor from Figure 3 in longitudinal section.

[0026] Figure 1 shows a conventional rotor lamination 10 with inserted permanent magnets 12.

[0027] The rotor lamination 10 has a constant inside diameter and a constant outside diameter. As a result, the rotor lamination 10 has a constant radial thickness 14 when viewed over its circumference.

[0028] The permanent magnets 12 are distributed uniformly over the circumference of the rotor lamination 10. They each have a north pole N and an opposite south pole S. The permanent magnets 12 are arranged in such a way that their two magnet poles lie on the same radius. When viewed in the circumferential direction, the north pole and the south pole of the permanent magnets 12 are oriented alternately towards the centre of the rotor lamination 10.

[0029] This gives rise to the magnetic field profile illustrated by means of arrows in Figure 1.

[0030] Using the density of the arrows, Figure 1 shows that there is a high magnetic flux density in regions between the permanent magnets 12 on the inside of the rotor lamination 10. Figure 2 shows a cup-shaped rotor 16 of the kind known from the prior art. The rotor 16 has a motor shaft 18 and a support 20, which is connected to the motor shaft 18 for conjoint rotation therewith.

[0031] Furthermore, the rotor 16 has a stack of rotor laminations 10, which carry a plurality of permanent magnets 12 and are arranged on the support 20. The arrangement and alignment of the permanent magnets 12 in Figure 2 correspond substantially to that in Figure 1. To this extent, attention is drawn to the above explanations.

[0032] As shown in Figure 2, the outer contour of the support 20 is round.

[0033] The rotor laminations 10 are arranged on the support 20. They have round inner and outer contours. Accordingly, their radial thickness 14 is substantially constant over the entire circumference. Protrusions and / or indentations in the inner contour of the laminations and indentations and / or protrusions of the outer contour of the support which are complementary thereto, said indentations and protrusions serving as an anti-rotation safeguard and / or for assembly purposes, can optionally be provided.

[0034] In the case of the rotor 16 shown in Figure 2, the relative radial thickness 14 (relative to the outer circumference) of the rotor laminations 10 is less than in the case of the rotor lamination 10 from Figure 1 on account of the installation space. In more simple terms, it is necessary in the case of the exemplary embodiment shown in Figure 2 to save on lamination volume towards the inside in order to create additional installation space for the support 20.

[0035] However, the absence of ferromagnetic lamination material leads to earlier onset of magnetic saturation and this, in turn, may have a negative effect on the operating characteristics of the motor.

[0036] Figures 3 to 5 show an embodiment of a rotor 16 according to the invention. For identical or functionally identical features, the same reference signs as in the figures described previously are used and, to this extent, reference is made to the above explanations. The rotor 16 shown in Figures 3 to 5 is provided for use in a hydraulic pump 22. This is of course not to be understood to be limiting. Other fields of application are also conceivable.

[0037] Like the rotor 16 shown in Figure 2, the rotor 16 according to the invention also has a motor shaft 18 and a support 20, which is connected to the motor shaft 18 for conjoint rotation therewith. Furthermore, the rotor 16 also has a stack of rotor laminations 10, which are arranged on the support 20 and carry a plurality of permanent magnets 12.

[0038] As can be seen in Figures 3 to 5, the support 20 is cup-shaped. It has a base 24 and a shell 26.

[0039] In the exemplary embodiment, the support 20 consists of a plastics material. The base 24 and the shell 26 form a coherent injection moulding, which is moulded onto the rotor laminations 10 from the inside.

[0040] The base 24 is provided with a plurality of through-openings 28, which connect the volume arranged inside the support 20 to the outside of the rotor 16. For example inner cooling of the rotor 16 by a cooling fluid is thus made possible.

[0041] In the exemplary embodiment, the shell 26 of the support 20 has a round inner contour with a constant inside diameter. Furthermore, the shell 26 has a starshaped outer contour. This is illustrated in Figure 4.

[0042] The rotor laminations 10 are arranged on the support 20 in such a way that the inner contour rests directly against the outer contour of the shell 26. In corresponding fashion, the inner contour of the rotor laminations 10 is likewise of star-shaped design.

[0043] In the exemplary embodiment, the rotor laminations 10 have a round outside diameter, which forms the outer contour of the rotor 16.

[0044] The rotor 16 thus has a round inner and a round outer circumference. This has a positive effect on the running properties.

[0045] When viewed in the circumferential direction, the rotor laminations 10 have a radial thickness 14 which changes periodically. As shown in Figure 4, this varies between a minimum value 30 and a maximum value 32. The maximum value 32 lies on a radius which extends between two permanent magnets 12 that are adjacent in the circumferential direction. The minimum value 30, in contrast, lies on a radius which runs through the centre of a permanent magnet 12.

[0046] By virtue of this special configuration, the rotor 16 according to the invention has additional ferromagnetic lamination material in regions between the permanent magnets 12, in which (as illustrated in Figure 1 ) there is a high magnetic flux density, in comparison with the conventional rotor 16 in Figure 2.

[0047] By means of this, the magnetic return path can be implemented between two adjacent poles without the occurrence of saturation effects, and this, in turn, has a positive effect on the operation of the motor. There is no need to interfere with the external geometry of the rotor 16 for this purpose.

[0048] In the exemplary embodiment, as shown in Figure 4, the wall thickness of the support 20 in the regions in which the rotor laminations 10 have their maximum thickness is approximately half the wall thickness of the support 20 in the regions in which the rotor laminations 10 have their minimum thickness.

[0049] It has been found that a high mechanical stability of the support 20 can be achieved despite the large variation in wall thickness over the circumference. Here, the regions of the support 20 with a greater wall thickness act like reinforcing ribs.

[0050] Another special feature of the exemplary embodiment shown is that the outer contour of the support 20 changes between concave portions 34 and convex portions 36 when viewed in cross section. In corresponding fashion, the inner contour of the rotor laminations 10 is also formed with alternating concave and convex portions.

[0051] As can be seen by considering Figures 1 and 4 together, it is possible in this way to achieve a rotor lamination shape adapted to the profile of the magnetic field. This ensures that sufficient ferromagnetic lamination material is available in regions of high magnetic flux density.

[0052] Figure 5 shows a longitudinal section through an exemplary embodiment of a hydraulic pump 22 according to the invention as well as the rotor 16 according to the invention already described above as a component part of the hydraulic pump

[0053] 22.

[0054] In addition to the rotor 16, the hydraulic pump 22 has a stator 38 and a pump module 40. The pump module 40, in turn, has a pump housing 42 having a bearing portion 44, in which the motor shaft 18 is mounted.

[0055] In this case, the rotor 16 is arranged in such a way that the bearing portion 44 and the support 20 overlap one another in the axial direction. In other words, the bearing portion 44 projects into the cup-shaped rotor 16.

[0056] In the exemplary embodiment, the bearing portion 44 extends into the support 20 over more than half of the axial length of the latter. A particularly compact pump design is thereby achieved.

[0057] On the outside, the bearing portion 44 is provided with ribs 46 which extend in the axial direction. In the exemplary embodiment, four ribs 46 distributed uniformly around the circumference of the bearing portion 44 are provided. Figure 5 shows a rib 46 at the upper end and a rib 46 at the lower end of the bearing portion 44. The two other ribs 46 project into the plane of the drawing or out of said plane and are not illustrated in the drawing. It is of course also possible to provide more or fewer than four ribs 46. The number of ribs 46 can also be matched to the number of permanent magnets 12 or pole pairs of the rotor 16. The ribs 46 improve the mechanical stability, in particular rigidity, of the bearing portion 44.

[0058] As illustrated in Figure 5, a gap 48 is provided between the ribs 46 and the support 20. In the exemplary embodiment, this is about twice as wide as the height of the ribs 46.

[0059] It has been found that this gap geometry enables drag losses during the operation of the motor to be kept low and enables the assembly of the hydraulic pump 22 to be simplified.

Claims

Patent claims1 . Rotor for an electric motor, having a motor shaft (18), a support (20), which is connected to the motor shaft (18) for conjoint rotation therewith, and a stack of rotor laminations (10), which are arranged on the support (20) and carry a plurality of permanent magnets (12), wherein the rotor laminations (10) have a radial thickness (14) which changes periodically when viewed in the circumferential direction and which varies between a minimum value (30) and a maximum value (32), wherein the maximum value (32) lies on a radius which lies between two permanent magnets (12) that are adjacent in the circumferential direction, and the minimum value (30) lies on a radius which passes through the centre of a permanent magnet (12), wherein the support (20) has a constant inside diameter.

2. Rotor according to claim 1 , characterized in that the wall thickness of the support (20) in the regions in which the rotor laminations (10) have their maximum thickness is approximately half the wall thickness of the support (20) in the regions in which the rotor laminations (10) have their minimum thickness.

3. Rotor according to claim 1 or claim 2, characterized in that the outer contour of the support (20) changes between concave portions (34) and convex portions (36) when viewed in cross section.

4. Rotor according to any of the preceding claims, characterized in that the support (20) consists of plastic.

5. Rotor according to any of the preceding claims, characterized in that the rotor laminations (10) have a constant outer radius.

6. Hydraulic pump having a stator (38), a rotor (16) according to any of the preceding claims, and a pump module (40), wherein the pump module (40) has a pump housing (42) with a bearing portion (44) in which the motor shaft (18) is mounted.

7. Hydraulic pump according to claim 6, characterized in that the bearing portion (44) and the support (20) overlap in the axial direction.

8. Hydraulic pump according to claim 7, characterized in that the bearing portion (44) extends into the support (20) over more than half of the axial length of the latter.

9. Hydraulic pump according to any of claims 6 to 8, characterized in that the bearing portion (44) is provided on the outside with ribs (46) which extend in the axial direction.

10. Hydraulic pump according to claim 9, wherein a gap (48) is provided between the ribs (46) and the support (20), wherein the gap (48) has a width which corresponds at least to the rib height.

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