Rotor for electric machine

Abstract

The invention relates to a rotor (10) for an electric machine, in particular for an electric motor, comprising a one-piece body (12); a stack (14) of rotor laminations (16) embedded in the body (12) and having a plurality of magnet slots (20); and a plurality of permanent magnets (22) held in the magnet slots (20), the magnet slots (20) being closed at each axial end by the main body (12).

Description

Technical Field

[0001] The present invention relates to a rotor for an electric machine, in particular an electric motor. Background Art

[0002] The rotor is particularly used in an electric motor for driving a hydraulic pump, for example in a motor vehicle, to provide a volumetric flow of hydraulic oil supplied to a clutch actuator, a gearbox actuator, a clutch cooling system, a gearbox lubrication system, etc.

[0003] Rotors with a body consisting entirely of injection-molded plastic are known. Embedded in the plastic are ferromagnetic particles, which are appropriately magnetized to create a plurality of permanent magnets with appropriate polarization.

[0004] Also known are rotors in which a stack of rotor laminations is mounted on a metal shaft, and the permanent magnets are held in the rotor laminations. Such rotors require more manufacturing effort but are characterized by a higher magnetic field strength. Summary of the Invention

[0005] The object of the present invention is to provide a rotor that includes a stack of rotor laminations and can be manufactured with less effort.

[0006] According to the present invention, this object is achieved by a rotor for an electric machine (in particular for an electric motor), which rotor includes a one-piece body; a stack of rotor laminations that are embedded in the body and have a plurality of magnet slots; and a plurality of permanent magnets held in the magnet slots, wherein the magnet slots are closed by the body at each axial end.

[0007] According to the present invention, the above object is also achieved by providing a method for manufacturing a rotor for an electric machine (in particular for an electric motor), the method having the following steps: assembling a stack of rotor laminations, each rotor lamination having a plurality of openings such that a plurality of magnet slots are formed. Pushing ferromagnetic bodies into each magnet slot. Subsequently, placing the stack of rotor laminations equipped with ferromagnetic bodies into an injection mold, and encapsulating the stack of rotor laminations with a plastic material to form a body that extends at least in some sections in the radial direction up to the magnet slots.

[0008] The present invention is based on the basic concept that instead of using discrete components to close the magnet slots at the axial ends of the magnet slots so that the permanent magnets are axially held therein, the magnet slots are closed by a section of the body, and the section of the body also serves as a support for the rotor laminations. The section of the body that closes the magnet slots is manufactured during the manufacturing process of the body, that is, in the same working step, in particular by appropriately forming the cavity of the injection mold. Thus, the body has a "closing element" that is formed integrally with the body and closes the magnet slots at the axial ends of the magnet slots.

[0009] According to one configuration of the invention, it is provided that the body extends axially into the magnet slots. This results in a form-fitting connection that is effective in the radial direction.

[0010] The body can axially extend further outwards at the axial end of the rotor than the magnet slots, such that the stack formed by the rotor laminations is axially clamped and firmly fixed in the axial direction.

[0011] According to one configuration of the invention, it is provided that the body forms a planar end face, such that if the rotor is a wet rotor, frictional losses are minimized.

[0012] The body can expose some of the magnet slots on at least one side of the rotor, such that the wall of the injection mold serves as an axial contact surface for the ferromagnetic bodies that are pushed into the magnet slots. This allows the ferromagnetic bodies to be positioned very precisely in the axial direction.

[0013] The body preferably extends outwards to such an extent that the magnet slots are axially covered at their centers. This produces sufficient radial coverage with the ferromagnetic bodies, while ensuring that on the sides of the magnet slots that face away from each other in the circumferential direction, the regions of the ferromagnetic bodies are not covered, such that they can support themselves on the wall of the injection mold.

[0014] The body can be can-shaped and have a plurality of through-holes that extend from the interior space of the body to the axial end face. The through-holes allow fluid circulation, by means of which waste heat can be removed from the interior of the electric motor.

[0015] According to one configuration of the invention, it is provided that the rotor laminations are exposed at the outer circumference of the rotor, such that the air gap between the rotor laminations and the stator surrounding the rotor remains as small as possible.

[0016] A rotor shaft is preferably provided that is injection-molded into the body in a form-fitting manner. This has the advantage that no separate step is required to install the rotor shaft.

[0017] According to one configuration of the invention, it is provided that the ferromagnetic bodies are pushed into the magnet slots in an unmagnetized state and are magnetized only after the body has been molded onto the stack of rotor laminations. This has the advantage that introducing the ferromagnetic bodies into the magnet slots and injection molding are both very easy, since there is no need to handle a magnetized stack of rotor laminations.

[0018] According to one configuration, it is provided that the body is provided with geometric positioning formations. The positioning formations, such as a plurality of grooves on the side surface of the body, ensure precise circumferential positioning of the rotor when the rotor is placed in the mold to magnetize the ferromagnetic bodies. Description of the Drawings

[0019] The invention will now be described based on two embodiments shown in the drawings. In the drawings:

[0020] Figure 1 Shows a longitudinal section of a rotor according to a first embodiment of the present invention;

[0021] Figure 2 Shows Figure 1 a plan view of the rotor in

[0022] Figure 3 Shows Figure 1 a first perspective view of the rotor in

[0023] Figure 4 Shows Figure 1 a bottom view of the rotor in

[0024] Figure 5 Shows Figure 1 a second perspective view of the rotor in

[0025] Figure 6 Shows a longitudinal section of a rotor according to a second embodiment of the present invention;

[0026] Figure 7 Shows Figure 6 a side view of the rotor in

[0027] Figure 8 Shows Figure 6 a perspective view of the rotor in

[0028] Figure 9 Shows Figure 6 a plan view of the rotor in

[0029] Figure 10 Shows Figure 6 a bottom view of the rotor in; and

[0030] Figure 11 Shows in an enlarged scale Figure 10 detail XI in Detailed Description

[0031] Figures 1 to 5 Shows a rotor 10 according to a first embodiment, which is intended to be used with a stator of an electric motor and is used to drive a hydraulic pump, for example in a vehicle driveline, for example to switch an actuator or lubricate or cool components.

[0032] The rotor 10 has a pot-shaped or cup-shaped body 12, which is made of plastic and is injection-molded.

[0033] The body 12 extends along the inner surface of a stack 14 of rotor laminations 16, which are held firmly against the body. The rotor laminations 16 are made of ferromagnetic material.

[0034] Each rotor lamination 16 is provided with a plurality of recesses 18 which together form a plurality of magnet slots 20 that extend axially through the stack 14. A permanent magnet 22 is disposed in each magnet slot.

[0035] The magnet slots 20 are closed at their two axial ends by the body 12, specifically, in each case by a flange 24 which is formed integrally with the body 12 and extends radially beyond the magnet slot up to the outer periphery of the stack 14 of rotor laminations 16. In this way, it is ensured that the permanent magnet 22 is fixed in the magnet slot 20 in the axial direction.

[0036] As can be seen in Figure 1 the left flange 24 slightly extends into the magnet slot 20 such that a form - fit connection is obtained there.

[0037] It can also be provided that the flange on the right side of the stack 14 of rotor laminations 16 extends into the magnet slot 20 and ends there.

[0038] The pot - shaped body 12 also has a base 26 which here serves to receive the rotor shaft 28. The rotor shaft 28 is injection - molded into the base 26 of the body 12.

[0039] A plurality of through - holes 30 are also provided in the base 26 through which hydraulic fluid can enter the interior space from the outside of the rotor and vice versa.

[0040] As can be seen particularly in Figure 3 and Figure 5 the flange 24 forms a flat end face on the respective side of the rotor 10 which extends almost up to the outer peripheral portion of the rotor 10. The outer peripheral portion itself is formed by the outer peripheral surface of the stack 14 of rotor laminations 16 that is exposed.

[0041] In principle, the permanent magnets 22 can be pushed into the magnet slots 20 of the stack 14 of rotor laminations 16, and then the stack can be placed in an injection mold where it is encapsulated with the material forming the body 12. However, according to a preferred embodiment, unmagnetized bodies of ferromagnetic material are respectively pushed into each magnet slot 20. Subsequently, the stack 14 equipped with such ferromagnetic bodies is placed in an injection mold and encapsulated with the material forming the body 12. Only then are the ferromagnetic bodies magnetized by an external coil to form the permanent magnets 22.

[0042] Figures 6 to 11 A rotor according to a second embodiment is shown. The same reference numerals are used for the components and features known from the first embodiment and are referred to the above explanations to that extent.

[0043] The difference between the first and second embodiments is that, in the case of the second embodiment, the magnet slots 20 are only completely or almost completely covered by the flange 24 on one side (here on the side of the base 26), and are not completely covered on the other side (i.e., the side facing away from the base 26).

[0044] As can be seen in Figure 10 , when observed in a sectional view or an end view, the magnet slots have an elongated cross-section. Their direction of extension is perpendicular to or tangent to the radius r passing through their centers. Therefore, the ends of each magnet slot 20 that are spaced apart from each other in the circumferential direction are located at a radius R that is greater than the radius r on which the center of each magnet slot lies. The body 12, more precisely the flange 24, is only formed up to such a radius (here the radius r) on one side of the rotor 10, such that some of the magnet slots 20 are not covered. In other words, some of the magnet slots 20 are exposed, specifically on the sides that are spaced apart from each other in the circumferential direction. These are indicated by reference numeral 21 in Figure 11 . Accordingly, some of the ferromagnetic or permanent magnets 22 arranged in the magnet slots 20 are also exposed.

[0045] As a result, the injection mold can be designed such that the ferromagnetic bodies 22 can abut against the wall of the injection mold. As a result, the ferromagnetic bodies 22 are precisely positioned axially. On the opposite side, the flange 24 ensures that the ferromagnetic bodies 22 are fastened axially. It is not absolutely necessary for the flange 24 to completely close the magnet slots 20 there.

[0046] The rotor 10 or its body 12 is provided with a plurality of geometric positioning and forming portions 40. The positioning and forming portions are here formed as grooves 40 extending axially in the side surface of the body 12. These ensure the precise circumferential positioning of the rotor 10 when the rotor 10 is placed in the mold for magnetizing the ferromagnetic bodies 22.

Claims

1. A rotor (10) for an electric machine, in particular for an electric motor, comprising a one-piece body (12); a stack (14) of rotor laminations (16), the rotor laminations (16) being embedded in the body (12) and having a plurality of magnet slots (20); and a plurality of permanent magnets (22) held in the magnet slots (20), the magnet slots (20) being closed by the body (12) at each axial end.

2. The rotor (10) according to claim 1, characterized in that, The body (12) extends axially into the magnet slots (20).

3. The rotor (10) according to any one of the preceding claims, characterized in that, The body (12) axially extends more outwardly than the magnet slots (20) at the axial ends of the rotor (10).

4. The rotor (10) according to any one of the preceding claims, characterized in that The body (12) forms a planar end face.

5. The rotor (10) according to any one of the preceding claims, characterized in that, The body (12) exposes some of the magnet slots (20) on at least one side of the rotor (10).

6. The rotor (10) according to claim 5, characterized in that, The body (12) extends outwardly such that the magnet slots (20) are axially covered at their centers.

7. The rotor (10) according to any one of the preceding claims, characterized in that, The body (12) is pot-shaped and provided with a plurality of through-holes (30) that extend from the interior space of the body (12) to the axial end face.

8. The rotor (10) according to any one of the preceding claims, characterized in that The rotor laminations (16) are exposed at the outer periphery of the rotor (10).

9. The rotor (10) according to any one of the preceding claims, characterized in that, A rotor shaft (28) is provided and injection-molded in a form-fitting manner into the body (12).

10. The rotor (10) according to any one of the preceding claims, characterized in that, The body (12) is formed of plastic and is formed as one piece.

11. The rotor (10) according to any one of the preceding claims, characterized in that, The body (12) is provided with geometric positioning forming parts (40).

12. A method of manufacturing a rotor (10) for an electric machine, in particular for an electric motor, is carried out by the following steps: - Assembling a stack (14) of rotor laminations (16), each of the rotor laminations (16) having a plurality of openings (18) such that a plurality of magnet slots (20) are formed, - Pushing ferromagnetic bodies into each of the magnet slots (20), - Placing the stack (14) of rotor laminations (16) fitted with the ferromagnetic bodies into an injection mold, - Encapsulating the stack (14) of rotor laminations (16) with a plastic material to form a body (12), the body (12) extending radially in at least some sections up to the magnet slots (20).

13. The method according to claim 12, characterized in that, After the body (12) has been molded onto the stack (14) of rotor laminations (16), the ferromagnetic bodies are pushed into the magnet slots (20) in an unmagnetized state and magnetized.

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