Method for manufacturing a rotor of an electric drive unit

Abstract

A method for manufacturing a rotor (1) of an electric drive unit, comprising the following process steps: a) providing a rotor lamination stack (2); b) manufacturing a cover plate (3) with a crown structure (4) by injection molding, wherein the cover plate (3) is made of a thermoplastic material; c) mounting the cover plate (3) on an axial end face of the rotor lamination stack (2); d) manufacturing a pre-assembly (7) by axially mounting permanent magnets (5) in magnet receiving pockets (6) of the rotor lamination stack (2); e) inserting the pre-assembly (7) into an injection mold; f) rotationally fixing the pre-assembly (7) in the injection mold by an interference fit with anti-rotation device to the pre-assembly (7) and via the crown structure (4) of the cover plate (3); g) manufacturing a media-tight casing (9) of the rotor (1) by overmolding the pre-assembly (7), wherein the casing (9) is made of a thermoplastic material consists;andh) Demolding of the overmolded rotor (1) from the injection mold.;

Description

[0001] The invention relates to a method for manufacturing a rotor of an electric drive unit according to claim 1, as well as a rotor according to claim 12 and a pump with such a rotor.

[0002] It is generally known that rotors of electric drive units, particularly those used in fluid pumps, must be protected from liquids or gases. The rotor, especially the lamination stack, is protected from liquids or gases by a plastic overmolding or a housing. In practice, the lamination stack is usually overmolded using a single-stage process with thermosets. Due to their viscosity, the liquid thermosets can flow into the mold cavity at low pressures. However, due to the viscosity, complete encapsulation of the components using a single-stage overmolding process is not possible, as there is a risk of the components sinking in the liquid plastic. Therefore, a two-stage overmolding process is necessary. In the two-stage overmolding process, the joint between the two thermoset shell components adheres only loosely to each other, and a metallurgical bond is not formed.Furthermore, typical temperature fluctuations can easily lead to the contact point breaking down, allowing corrosive media to penetrate the rotor's lamination stack. Another disadvantage of using thermosets for overmolding is the long curing cycle time, which results in high process costs. Additionally, undesirable burrs form at the mold parting lines, and sprue overhangs necessitate costly mechanical rework.

[0003] The object of the invention is to provide a method for manufacturing a rotor for an electric drive unit, which reduces cycle times for curing and thereby avoids high process costs, prevents undesirable burrs at the tool parting lines, avoids costly mechanical rework, and, for cost reasons, ensures fast, reliable, and low-rejection production in large series. Furthermore, the invention provides a rotor for an electric drive unit and a pump with such a rotor.

[0004] This problem is solved according to the invention with regard to the method by the features according to claim 1, with regard to the rotor by the features according to claim 12 and with regard to the pump by the features according to claim 15.

[0005] In accordance with the present invention, a method for manufacturing a rotor of an electric drive unit, in particular an electric motor, is proposed, comprising the following process steps: a) Providing a rotor lamination package; b) Production of a cover plate with a crown structure by injection molding c) Mounting the cover disc on an axial end face of the rotor lamination stack; d) Production of a pre-assembly by axially mounting permanent magnets in magnet pockets of the rotor lamination stack; e) Inserting the pre-assembly into an injection mold; f) Rotational fixation of the pre-assembly in the injection mold by means of an interference fit with anti-rotation device to the pre-assembly and via the crown structure of the cover plate; g) Production of a media-tight coating of the rotor by overmolding the pre-assembly and h) Demolding of the overmolded rotor from the injection mold.

[0006] In the inventive method for manufacturing a rotor, a rotor lamination stack is provided. The rotor lamination stack is designed as a so-called T-rotor with internal magnet pockets in which the permanent magnets are mounted. Alternatively, the rotor lamination stack can also be designed as a so-called I-rotor with openings in the magnet pockets in which the permanent magnets are mounted. The permanent magnets can be mounted in the rotor lamination stack in any direction known to those skilled in the art (tangential, radial, axial).

[0007] A cover plate with a crown structure is manufactured by injection molding and attached to an axial end face of the rotor lamination stack by means of a press-fit, adhesive, or other fastening method known to those skilled in the art. Permanent magnets are then axially mounted in magnet pockets of the rotor lamination stack, thus creating a pre-assembly.

[0008] The pre-assembly is then placed in an injection mold and rotationally secured to the pre-assembly by an interference fit with anti-rotation device and via the crown structure of the cover plate. In an overmolding process, a media-tight encapsulation of the rotor is created by overmolding the pre-assembly, protecting the rotor from liquids, gases, or other corrosive media. A chamfer is formed on one outer diameter of the cover plate. The media-tight encapsulation of the rotor offers the advantage of high balancing quality. The media-tight encapsulation does not completely cover the pre-assembly. The axial end face of the cover plate is left uncovered by the encapsulation. The rotor's tightness in this area is achieved through the chamfered edge of the cover plate and by preheating the pre-assembly before overmolding.

[0009] In a final process step, the overmolded rotor is demolded from the injection mold and thus ejected from the injection mold.

[0010] According to an advantageous design, the crown structure of the cover plate ensures XY positioning of the pre-assembly relative to the axis of rotation in the injection molded part. This prevents displacement of the pre-assembly during overmolding and thus avoids imbalance.

[0011] In a further advantageous embodiment, the casing and / or the cover plate consist of a thermoplastic polymer material, in particular impact-modified polyphenylene sulfide (PPS). The impact modifier added to the PPS prevents cracks in the casing and / or the cover plate. Further advantages of using PPS as the base material for the casing and / or the cover plate include chemical resistance to corrosive media and increased temperature resistance.

[0012] In contrast to the use of thermoset plastics, encasing the rotor with thermoplastic material allows for a material bond or weld between the cover plate and the encasing. Furthermore, the cycle times for curing thermoplastic materials are shorter than with thermoset materials, leading to reduced process costs. Another advantage of thermoplastic materials is that they do not produce unwanted burrs at the mold parting lines or from the sprue, thus eliminating the need for costly post-processing.

[0013] According to a further advantageous embodiment, the media-tight casing on the outer diameter of the rotor is thin-walled, at least in the area of ​​the permanent magnets. This allows the magnetically ineffective air gap between the permanent magnets and the stator winding to remain small. The casing is thin-walled, i.e., less than 1 mm. "Thin-walled" here refers to a reduced wall thickness of the casing in the area of ​​the permanent magnets compared to the remaining wall thickness of the casing outside this area.

[0014] In a further advantageous embodiment, at least two injection points are located rotationally within the thin-walled area. This ensures complete filling with the thermoplastic material. The at least two injection points are arranged symmetrically to the rotor's central axis to prevent displacement of the pre-assembly during the injection molding process. Additionally, the crown structure on the cover plate prevents rotation of the pre-assembly during the filling process. Using only one injection point would cause the melt to shift or tilt the pre-assembly.

[0015] Alternatively, a single injection point must be placed on an additional rotor feature (e.g., impeller) located sufficiently far from the pre-assembly so that the flow fronts are initially merged and the resulting combined flow front flows precisely and uniformly cylindrically along the pre-assembly. When filling via multiple injection points, it is crucial for balance quality that the pre-assembly to be overmolded is neither displaced in the XYZ directions, nor rotated, nor tilted by the melt. For a single-stage overmolding process, such as with thermoset plastic material, this cannot be reliably guaranteed.

[0016] According to a further advantageous embodiment, the pre-assembly is supported relative to the injection mold in the z-direction across the entire surface of the cover plate. This ensures that the permanent magnets remain securely positioned in the magnet pockets during the injection molding process.

[0017] In a further advantageous embodiment, a tapered chamfer is formed on one outer diameter of the cover disc. This tapered chamfer facilitates easier melting of the thin amorphous surface layer of the cover disc. Slight burrs in the parting line further optimize this effect.

[0018] According to a further advantageous embodiment, the rotor lamination stack has stepped lamination sections in the edge region. The stepping in the edge region avoids a notch effect, which is the origin of potential cracking during temperature changes, and reduces the risk of the outermost laminations of the rotor lamination stack being bent by flowing molten metal.

[0019] In a further advantageous embodiment, a bearing bushing is centered on the pre-assembly within the injection mold. Precise centering of the bearing bushing on the pre-assembly enables high balancing quality. The overmolding creates a mechanical connection to the bearing bushing. The bearing bushing can be made of a metallic material or of another material known to those skilled in the art.

[0020] According to a further advantageous embodiment, the bearing bushing and the pre-assembly are preheated before overmolding. Preheating is carried out to approximately 150°C. However, other preheating temperatures are also possible. Preheating optimizes the welding of the cover plate to the thermoplastic material and reduces internal stresses in the overmolding that could lead to cracking.

[0021] In a further advantageous embodiment, a vent is provided in the injection mold at the end of the flow path. This vent can be designed as an ejector or a vent hole. The vent in the injection mold allows the air to escape completely and prevents defects. A brief period of air retention before the vent optimizes the weld by locally heating the chamfer at the end of the mold.

[0022] Furthermore, the invention relates to a rotor of an electric drive unit with a rotor lamination stack which is enclosed in a media-tight manner by a casing, wherein a cover plate with a crown structure is mounted on an axial end face of the rotor lamination stack, wherein permanent magnets are axially mounted in magnet receiving pockets in the rotor lamination stack and form a pre-assembly, wherein the pre-assembly is inserted into an injection molding tool, wherein a rotational fixation of the pre-assembly in the injection molding tool is achieved by an interference fit with anti-rotation device to the pre-assembly and via the crown structure of the cover plate, wherein the media-tight enclosure of the rotor is achieved by overmolding the pre-assembly and wherein the overmolded rotor is demolded from the injection molding tool.

[0023] In an advantageous embodiment, the bearing bushing is arranged in a recess for a shaft in the rotor lamination stack, in particular by injection molding. However, the bearing bushing can also be fastened in the rotor in any manner known to those skilled in the art.

[0024] According to a further advantageous embodiment, the casing and / or the cover plate are made of a thermoplastic material, in particular impact-modified polyphenylene sulfide (PPS), and / or the rotor lamination stack consists of magnetized sheets, and the permanent magnets are rare-earth magnets and / or polymer-bonded magnets. The impact modifier added to the PPS prevents cracks in the casing and / or the cover plate. Further advantages of using PPS as the base material for the casing and / or the cover plate are its chemical resistance to corrosive media and its increased temperature resistance.

[0025] Furthermore, the invention relates to a pump with a previously disclosed rotor of an electric drive unit, in particular a cooling or heating medium pump, preferably for a motor vehicle or a household appliance. The rotor of an electric drive unit according to the invention can also be used in an oil pump or an oil mist separator. The advantages and preferred embodiments mentioned in connection with the rotor also apply accordingly to the electric drive unit and also to the (fluid) pump or oil pump equipped with the electric drive unit, as well as the oil mist separator equipped with the electric drive unit.

[0026] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying drawings. These show: Fig. 1: an overmolding of the rotor according to the invention; Fig. 2: a top view of the rotor according to Fig. 2; Fig. 3: a detailed view of the distal end of the rotor according to the invention Fig. 1; Fig. 4: a top view of the rotor according to the invention Fig. 3; Fig. 5: a sectional view of the rotor according to the invention Fig. 3.

[0027] Fig. Figure 1 shows an overmolding of the rotor (1) of an electric drive unit according to the invention, comprising a rotor lamination stack (2) (not shown here) on which a cover plate (3) with a crown structure (4) is mounted on an axial end face and which forms a pre-assembly (7) by receiving permanent magnets (5) (not shown here) in magnet receiving pockets (6) (not shown here). The pre-assembly (7) is placed in an injection mold and rotationally fixed to the pre-assembly by an interference fit with anti-rotation device and via the crown structure of the cover plate. In an overmolding process, a media-tight coating (9) of the rotor is produced by overmolding the pre-assembly (7). The media-tight coating (9) of the rotor (1) does not completely cover the pre-assembly (7). The axial end face of the cover plate (3) is recessed by the coating (9).A tapered chamfer (8) is formed on the outer diameter of the cover plate (3), facilitating the melting of the thin amorphous surface layer of the cover plate (3) and bonding with the casing (9) during the overmolding process. When inserting the pre-assembly (7) into the injection mold, a bearing bushing (12) can also be inserted. The bearing bushing (12) is placed in a recess (13) for a shaft in the pre-assembly (7) and centered in the injection mold relative to the pre-assembly (7). The pre-assembly (7) and the bearing bushing (12) can be preheated before overmolding. Alternatively, the bearing bushing (12) can also be subsequently installed in the rotor (1).

[0028] Fig. Figure 2 shows a top view of the rotor according to Fig. 2, comprising a cover plate (3) with a crown structure (4) mounted on an axial end face of the pre-assembly (7). The pre-assembly (7) is inserted into an injection mold and rotationally fixed to the pre-assembly by an interference fit with anti-rotation device and via the crown structure of the cover plate. In an overmolding process, a media-tight coating (9) of the rotor is produced by overmolding the pre-assembly (7). The media-tight coating of the rotor does not completely cover the pre-assembly. The axial end face of the cover plate (3) is left uncoated by the coating. The coating (9) only fuses with the edge region of the cover plate (3). When inserting the pre-assembly (7) into the injection mold, a bearing bushing (12) can also be inserted into the injection mold.The bearing bushing (12) is inserted into a recess (13) for a shaft in the pre-assembly (7) and centered in the injection molding tool relative to the pre-assembly (7). The pre-assembly (7) and the bearing bushing (12) can be preheated before overmolding. Alternatively, the bearing bushing (12) can also be subsequently installed in the rotor (1).

[0029] Fig. Figure 3 shows a detailed view of the distal end of the rotor (1) according to the invention for an electric drive unit, which has a media-tight encapsulation (9) of the rotor (1) by overmolding the pre-assembly (7). The encapsulation (9) of the rotor (1) is thin-walled, at least in the area of ​​the permanent magnets (5) (not shown here). In the thin-walled area, at least two injection points (10) are arranged symmetrically to ensure complete filling of the rotor (1) with the thermoplastic material. The at least two injection points (10) are arranged symmetrically to prevent displacement or tilting of the pre-assembly (7) during the injection molding process. A chamfer (8) is formed on the outer diameter of the cover plate (3). The overmolded rotor (1) has an injected bearing bushing (12). Alternatively, the bearing bushing (12) can also be mounted after the overmolding process.

[0030] Fig. Figure 4 shows a top view of the rotor (1) according to the invention. Fig. 3, comprising a media-tight encapsulation (9) of the rotor (1) by overmolding the complete pre-assembly (7), at least two injection points (10) which are arranged rotationally in the thin-walled area, a tapered chamfer (8) on the outer diameter of the cover disc (3) and a bearing bushing (12).

[0031] Fig. Figure 5 shows a sectional view of the rotor (1) according to the invention. Fig.3, comprising a rotor lamination stack (2) on which a cover disk (3) with a crown structure (4) is mounted on an axial end face and which forms a pre-assembly (7) by receiving permanent magnets (5) in magnet receiving pockets (6). The cover disk (3) has a tapered chamfer (8) on its outer diameter. The rotor lamination stack (2) has stepped lamination stack sections (11) in the edge region. In the pre-assembly (7), a bearing bushing (12) is mounted centered towards the pre-assembly in a recess (13) for a shaft. The pre-assembly (7) is surrounded by a media-tight casing (9) made of thermoplastic material. Reference symbol list 1 Rotor 2 Rotor lamination package 3 Cover plate 4 crown structure 5 permanent magnets 6 magnetic recording pockets 7 Front assembly 8th phase 9 Sheathing 10 Injection point 11 Stepped sheet metal package cuts 12 Bearing bushing 13 Exclusion

Claims

[1] Method for manufacturing a rotor (1) of an electric drive unit, in particular an electric motor, comprising the following process steps: a) Providing a rotor lamination package (2); b) Production of a cover plate (3) with a crown structure (4) by injection molding; c) Mounting the cover disc (3) on an axial end face of the rotor lamination stack (2); d) Production of a pre-assembly (7) by axially mounting permanent magnets (5) in magnet receiving pockets (6) of the rotor lamination stack (2); e) Inserting the pre-assembly (7) into an injection mold; f) rotational fixation of the pre-assembly (7) in the injection molding tool by means of an interference fit with anti-rotation device to the pre-assembly (7) and via the crown structure (4) of the cover plate (3); g) Production of a media-tight coating (9) of the rotor (1) by overmolding the pre-assembly (7) and h) Demolding of the overmolded rotor (1) from the injection mold. [2] Method according to claim 1, characterized by , that an XY positioning of the pre-assembly (7) to the axis of rotation in the injection mold is achieved by the crown structure (4) of the cover plate (3). [3] Method according to claim 1, characterized by , that the casing (9) and / or the cover plate (3) are made of a thermoplastic polymer material, in particular impact-modified polyphenylene sulfide (PPS). [4] Method according to claim 1, characterized by , that the media-tight casing (9) on the outer diameter of the rotor (1) is thin-walled at least in the area of ​​the permanent magnets (5). [5] Method according to claims 1 and 4, characterized by , that at least two injection points (10) are located in the thin-walled area during rotation. [6] Method according to any one of the preceding claims, characterized by, that the pre-assembly (7) is supported in the z-direction relative to the injection mold over the entire surface of the cover plate (3). [7] Method according to claims 1 and 6, characterized by , that a tapered chamfer (8) is formed on an outer diameter of the cover disc (3). [8] Method according to claim 1, characterized by , that the rotor lamination stack (2) has stepped lamination stack cuts (11) in the edge area. [9] Method according to claim 1, characterized by , that a bearing bushing (12) is centered to the pre-assembly (7) in the injection molding tool. [10] Method according to claim 1, characterized by , that the bearing bushing (12) and the pre-assembly (7) are preheated before overmolding. [11] Method according to claim 1, characterized by , that a vent is provided in the injection molding tool at the flow path end of the casing (9). [12] Rotor (1) of an electric drive unit with a rotor lamination stack (2) which is completely and media-tightly surrounded by a casing (9), wherein a cover plate (3) with crown structure (4) is mounted on an axial end face of the rotor lamination stack (2), wherein permanent magnets (5) are axially mounted in magnet receiving pockets (6) in the rotor lamination stack (2) and form a pre-assembly (7), wherein the pre-assembly (7) is inserted into an injection mold, wherein a rotational fixation of the pre-assembly (7) in the injection mold is ensured by an interference fit with anti-rotation feature to the pre-assembly (7) and via the crown structure (4) of the cover plate (3), wherein the media-tight casing (9) of the rotor (1) is formed by overmolding the pre-assembly (7) and wherein the overmolded rotor (1) is demolded from the injection mold. [13] Rotor according to claim 12, characterized by, that the bearing bushing (12) is arranged in a recess (13) for a shaft in the rotor lamination stack (2), in particular injection molded. [14] Rotor according to claim 12, characterized by , that the casing (9) and / or the cover disc (3) are made of a thermoplastic polymer material, in particular impact-modified polyphenylene sulfide (PPS), and / or that the rotor lamination stack consists of magnetized sheets, and that the permanent magnets are rare earth magnets and / or polymer-bonded magnets. [15] Pump with an electric drive unit, in particular an electric motor, comprising a rotor according to one of the preceding claims.

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