METHOD FOR MANUFACTURING AN ELECTRIC MOTOR AND ELECTRIC MOTOR

Description

[0001] The invention relates to a method for manufacturing an electric motor which a housing which may include one or more housing covers, with a stator, a rotor with a rotating axis and a canned tube adjacent to the inner wall of the stator, which seals a fluid cooling device of the stator towards the rotor, exhibits.

[0002] The invention further relates to a similar electric motor.

[0003] Such electric motors are known. The canned tube serves to isolate the stator chamber from the rotor chamber, allowing a fluid to flow solely within the stator chamber in close proximity to the winding coils, without affecting the rotor. This is particularly relevant for cooling by a liquid that is introduced into the stator chamber when cold and discharged when heated. A thermal oil has proven especially suitable for this purpose.

[0004] DE 41 38 268 A1 describes, for example, an electric motor with water cooling in the stator compartment and air cooling in the rotor compartment. The windings located in the stator slots are directly cooled by the cooling water. The slot gaps in the stator lamination stack are sealed with a liquid-tight seal. Compared to cooling with thermal oil, the operating temperatures are limited to a range of 0°C to 100°C. A canned tube extending axially along the inner wall of the stator—as required in this invention—is not provided. The applicant explained that a canned tube requires space and outlined the associated disadvantages. This space can be created by increasing the air gap between the rotor and stator. However, this reduces the motor's power output and lowers its efficiency.

[0005] This problem was identified in EP 1 272 747 A1. For this reason, the central section of a slotted tube was designed with thinner walls than the side sections (at the axial ends of the electric motor) to which the thinner-walled central section must be connected.

[0006] The design and installation of such a slotted tube is very complex in the manufacture of an electric motor.

[0007] Documents EP 3 972 095 A1, JP 2019 068702 A and DE 10 2021 103985 A1 describe further examples of electric motors with canned tubes.

[0008] The object of the invention is to simplify the manufacture of an electric motor with stator, rotor and canned tube and to create a correspondingly simplified manufactured electric motor.

[0009] The problem is solved procedurally by the features of claim 1.

[0010] This relatively simple design of the electric motor ensures that the stator chamber and its cooling fluid are completely separated from the rotor chamber. It is particularly suitable for the use of thermal oil as the cooling fluid, and the rotor's rotation is not ineffectively affected by the cooling fluid. The cooling fluid can be circulated into and out of the stator chamber by a circulation system, which will not be discussed in detail here.

[0011] Basically, only a few simple steps are necessary to manufacture the electric motor according to the invention.

[0012] Initially, the rotor is not yet installed in the housing containing the stator, so the space designated for it remains empty. Instead, a heated, tubular preform is inserted into this area, featuring an opening at one end for gas pressure injection. The heating temperature of the thermoplastic material could typically be between 90°C and 150°C, considerably higher for PFA, but preferably just above the material's softening temperature.

[0013] The tubular preform can be effectively inflated by softening the thermoplastic material. This can begin with a gas pressure of, for example, 1 to 2 bar and end with a gas pressure of up to 40 bar. The housing with the stator then forms the final shape. Similar processes are known, for example, in the production of PET bottles. During this process, the wall thickness decreases, so that after cooling and hardening, a thin, formed canned tube is obtained that fits snugly against the stator, effectively keeping the distance between the stator and rotor very small. To prevent collapse under the subsequent pressure of the cooling fluid, it would be advantageous to ensure that the surface of the canned tube forms a bond with the inner surface of the stator. This bond could be, for example, a positive-locking or a material-locking connection.Without such further measures, the coolant in an electric motor with a very thin canned tube should be circulated at the lowest possible pressure during operation through a heat exchanger and the stator chamber. Nevertheless, an expansion tank is necessary because the coolant heats up and expands. The greatest heat generation occurs in the electric motor's coils. These are electrically insulated from the rest of the motor. Good electrical insulators are generally also good thermal insulators. Thus, an electric motor can be improved simply by creating a thermal bridge between the coil and the heat exchanger. This bridge can, in one possible form, be the coolant itself. In the simplest case, the heat exchanger is the smooth surface of the motor or a finned structure on its surface.

[0014] The remaining end cap, bottom, and / or neck (created by inflating the preform) with the gas pressure connection must be removed as excess material. These ends are referred to here as slugs. This results in a preferably predominantly cylindrical tube, but adapted to the inner wall of the stator, in contact with the stator.

[0015] Separating the slugs also creates space for the rotor, which can be inserted and stored in the usual way.

[0016] A major advantage of the inventive method for manufacturing an electric motor is therefore that the canned tube, with its final dimensions and especially its diameter, can be produced adapted to the geometric conditions within the housing. This completely eliminates the external manufacturing and forming processes for a canned tube, as well as its installation in the electric motor being manufactured.

[0017] Preferably, a thermoplastic, preferably polymeric, plastic is used as the preform.

[0018] It is important to ensure that the resulting canned tube can withstand the operating temperature of the electric motor. Commonly used plastics in similar blow molding processes include polyolefins, polyethylene (PE), and polypropylene (PP), which are primarily used for food packaging. Due to their low operating temperature, these are not particularly suitable for this application. Similarly, common polypropylenes and polycarbonates (PC) are only suitable for motors with low operating temperatures, but will suffice in most cases. Besides the common polyamides (PA6 and PA6.6), so-called high-performance thermoplastics are particularly suitable: polyphthalamide (PPA), PA 4.6, polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyetherketone (PEK), polyamide-imides (PAI), polysulfones (PSU, PES, PPSU), and perfluoroalkoxy polymers (PFA), to name just a few well-known materials.

[0019] In addition to the optionally provided positive-locking or material-locking connection between the surface of the slot tube and the inner surface of the stator, it is preferred that the preform has an adhesive or an adhesive surface on its outer circumference.

[0020] During curing, the canned tube forms a bond with the stator. This has the positive effect that, in particular, a large bond prevents the canned tube from collapsing under the cooling fluid pressure and also results in improved sealing at the ends.

[0021] Two different blow molding processes for a heated preform are known: stretch blow molding and extrusion blow molding. Both processes can be preferentially used in this manufacturing process for an electric motor according to the invention. According to Wikipedia, a) stretch blow molding, also known as injection stretch blow molding, is a process for producing hollow bodies that are stretched in the circumferential and longitudinal directions (e.g., PET bottles), and b) extrusion blow molding, also known as hollow body blow molding, is a plastics processing method for producing hollow bodies from thermoplastic materials. In the latter, the molten polymer is forced through the die via a screw conveyor, creating a tubular preform (extrusion). This is then transferred to a blow mold and shaped to the mold's internal contours by internal pressure (blow molding).Hollow bodies produced in this way are used both as primary packaging materials such as canisters or barrels and as technical components such as fuel tanks or ventilation ducts.

[0022] It is clearly evident that the inventors have succeeded in using interdisciplinary and unconventional methods in the production of an electric motor.

[0023] To limit the expansion of the preform during the inflation process into a slotted tube, it is advantageous to close the housing with at least one first housing cover during the introduction of gas pressure. After the slotted tube is complete, the first housing cover can be removed to cut off the slugs and install the rotor.

[0024] After forming the slotted tube, including removing the slugs and subsequently inserting the rotor into the rotor chamber, preferably at least one second bearing cover is attached to at least one end of the housing, in which a bearing for the rotor is integrated.

[0025] If a larger open space is provided to the side of the stator, in particular its laminated core, and the housing cover, it is advantageous to insert a support device for the slotted tube there before the introduction of the preform.

[0026] This support structure could, for example, be a ring covering the gap, the inner circumference of which corresponds to the inner circumference of the stator. This ensures that the canned tube, which then rests against the stator and the support, has the same diameter along its entire length. The support structure can also be removed after the canned tube has been manufactured.

[0027] It can also be advantageous to either repeat the process of blowing a preform multiple times or to carry it out as a multilayer or coextrusion process, so that the core tube is built up from several layers. Particularly advantageous is the ability for the layers to perform different functions during subsequent operation, for example, regarding sealing, insulation, or chemical properties. For instance, a material that bonds well with the lamination stack and support structure can be used towards the stator chamber. For another layer, a material is selected that exhibits particular resistance to the cooling medium and ensures a tight seal. Other layers can, for example, exhibit higher strength by being filled with a filler, especially a fibrous material such as glass fibers, carbon fibers, or similar.

[0028] In a further embodiment, polymers with different properties can be introduced separately in the axial and / or circumferential direction.

[0029] With regard to the electric motor according to the invention, the problem is solved by the features of claim 11 and in particular by the fact that the slotted tube inside the housing is produced from a (heated) preform made of a thermoplastic material by a stretch blow molding process or extrusion blow molding process.

[0030] The advantages of the electric motor to be manufactured, which were emphasized in the manufacturing process, naturally also apply here and should not be repeated unnecessarily.

[0031] As a purely functional feature, the advantage of a separate seal between the canned tube and the housing cover is noted, which prevents coolant from leaking from the stator chamber into the engine compartment, even when the canned tube expands thermally. The seal can, for example, be a simple O-ring embedded in the housing cover.

[0032] This means that the wall thickness only needs to be between 0.05 and 0.5 mm. The advantage of the small distance between the stator and rotor, resulting in high motor efficiency, is obvious. It is also particularly advantageous if the core tube has a constant wall thickness along its entire length.

[0033] The invention will now be explained in more detail using an exemplary embodiment and six figures.

[0034] This shows Figs. 1 to 5 an electric motor in 5 manufacturing steps, Figs. 6 and 6aa cross-section through a motor according to the invention and a detailed section.

[0035] Figs. 1 to 5 Figure 1 shows an embodiment of the manufacturing process for the electric motor in five intermediate steps. This embodiment relates in particular to a stretch blow molding process, although it can also refer analogously to an extrusion blow molding process.

[0036] Fig. 1 The housing 2 with stator 3 as the starting point and Fig. 5 Finally, the completed electric motor is shown. All illustrations show a longitudinal section.

[0037] The first step, in Fig. 1As shown, the housing 2, which already contains the stator 3 with its laminated core 16 and its windings 18, is closed with first housing covers 5.1. Prior to this, a support device 9 is inserted laterally to the laminated core 16, extending to the first housing covers 5.1 at each of the axial ends of the housing 2. In this embodiment, this support device is a ring that bridges the gap and has an inner diameter that corresponds to the diameter of the stator's inner wall 6.

[0038] In a housing cover 5.1 (in the Fig. 1(The housing cover shown on the left) leaves an opening through which a tubular preform 11 made of a thermoplastic material is inserted into the rotor chamber 7.2, which is still empty at this point. The preform is in a heated state at this stage, just above the material's softening temperature. The stator inner wall 6, the support structure 9, and recesses in the first housing covers 5.1 form a shape around the preform 11.

[0039] Because, as in Fig. 2As shown only schematically by an arrow, a gas pressure 12 is introduced into the preform, causing the preform to expand until it reaches the contours of the mold. The pressure can be increased during this process, for example, from approximately 1 to 2 bar to up to 40 bar. In the area of ​​the stator inner wall 6 and the support structure 9, a cylindrical tube section is formed, extending the entire length of the housing 2, which then hardens to form the future canned tube 10.

[0040] The preform has thus developed into a bottle-like shape, before which the "neck" and the "bottom", referred to in this application as butt 13, still need to be removed in order to form the final cylindrical slotted tube 10.

[0041] This will be done, as in Fig. 3As shown, the first housing covers 5.1 have been removed. This makes the slugs 13 easily accessible and cut off. Subsequently, it is also possible to carry out the stretch blow molding process or the extrusion blow molding process a second time. This gives the slotted tube a second layer, which can consist of a different material, possibly adapted to a different function.

[0042] This leads to the situation that in Fig. 4 The figure shows that the slotted tube 10 extends essentially over the length of the housing 2. A rotor chamber 7.2 has formed inside the slotted tube.

[0043] In the final step according to Fig. 5The electric motor 1 is completed. The rotor 4 is inserted into the canned tube 10. Then, second housing covers 5.2 are inserted and fastened at the ends of the housing 2. In the illustrated embodiment, bearings 8 for the rotor 4 are accommodated in the housing covers 5.2. Additionally, depending on requirements, a further seal for the cooling fluid circulating in the stator chamber 7.1 is provided by an additional ring seal 19 on the housing cover. As an alternative or additional option, the preform (see again here) can be used. Fig. 1 ) on the outer circumference be equipped with an adhesive 14 or an adhesive surface so that it firmly connects the slot tube to the stator inner wall 6 and the support devices 9.

[0044] In Fig. 6 For better understanding, a cross-section through the electric motor according to the invention is also shown. Fig. 6a Enlarges the circled area.

[0045] In Fig. 6 The housing 2, which surrounds the stator 3 with its laminated core 16 and winding coils 18, is clearly visible. The rotor 4 with its axis of rotation 20 lies at the center. The slotted tube 10, shown with a slightly thicker line, was produced from a preform 11 made of a thermoplastic material using a stretch blow molding or extrusion blow molding process. In reality, in this embodiment, it has a wall thickness that is as constant as possible, between 0.05 and 0.5 mm.

[0046] An example of a stator 3 with a distributed winding 18 is shown. It is understood that this method can also be applied to stators with other winding methods. Here, the concentrated winding or the hairpin winding technology are again examples. For short lamination stacks, it is sufficient if only the winding ends are cooled by the coolant. For longer machines, it is advantageous if the portion of the coil located in the slot, or the lamination stack in the rotor area, is also cooled by the coolant. For this purpose, optional cross-sectional areas are created in the housing 2, in the lamination stack 16, or along the coil 18 in the slot of the lamination stack 16. For a distributed winding, the location in the slot near the tooth 17 of the lamination stack 16 is suitable.

[0047] In the enlarged section, the teeth 17 of the laminated core and the coils 18 are particularly visible. Near the slot 10, a fluid channel 15 remains next to each winding 18; this channel is part of the fluid cooling system. Thermal oil flows through the fluid channel 15, thereby cooling the coils. Reference symbol list

[0048] 1 electric motor 2 Housing 3 stator 4 rotor 5.1 First case cover 5.2 Second case cover 6 Stator inner wall 7.1 Stator space 7.2 Rotor chamber 8 Storage 9 Support device 10 Split pipe 11 preform 12 Gas pressure inlet (arrow) 13 Butzen 14 Adhesive on outer circumference of preform 15 Fluid cooling system, fluid channel 16 Sheet metal package 17 Tooth 18 Winding spools 19 seal 20 axis of rotation

Claims

1. Method for producing an electric motor which comprises: - a housing (2) with a stator (3), the housing (2) being able to comprise one or more housing covers (5.1, 5.2), - a rotor (4) with an axis of rotation (20), and - a gap tube (10) that bears against the inner stator wall (6) of the stator (3) and seals a fluid cooling unit (15) of the stator (3) towards the rotor (4), wherein within the rotor space (7.2) provided for the rotor (4) but still empty inside the housing (2), a tubular preform (11) made of a thermoplastic material, heated to a temperature above the softening temperature of the material, is introduced, a gas pressure (12) is introduced into the preform (11) such that the preform (11) expands radially until it abuts the stator (3), conforms to it in a tubular manner and thus at least partially forms the gap tube (10), any flash (13) that occurs at the ends of the preform (11) inflated into a gap tube (10) is removed, and finally the rotor (4) is mounted in the rotor space (7.2), and that before the introduction of the preform (11), a supporting device (9) for the gap tube (10) is arranged at least in the axially lateral space between the stator (3), in particular its laminated core (16), and the housing cover.

2. Method according to claim 1, characterized in that a thermoplastic, preferably polymeric plastic is used as the preform (11).

3. Method according to claim 1 or 2, characterized in that the preform (11) has an adhesive (14) or an adhesive surface on its outer circumference.

4. Method according to one of claims 1 to 3, characterized in that the preform (11) made of thermoplastic material is transformed into a gap tube (10) in a stretch blow-moulding process.

5. Method according to one of claims 1 to 3, characterized in that the preform (11) made of thermoplastic material is transformed into a gap tube (10) in an extrusion blow-moulding process.

6. Method according to one of claims 1 to 5, characterized in that the housing (2) is closed by at least a first housing cover (5.1) during the introduction of the gas pressure (12).

7. Method according to one of claims 1 to 6, characterized in that the rotor (4) is mounted at least in a second housing cover (5.2).

8. Method according to one of claims 1 to 7, characterized in that the gap tube (10) is constructed from several layers by inflating several preforms (11).

9. Method according to claim 8, characterized in that the different layers assume different functions.

10. Electric motor with: - a housing (2) with a stator (3), - a rotor (4) with an axis of rotation (20), and - a gap tube (10) that bears against the inner stator wall (6) of the stator (3) and seals a fluid cooling unit (15) of the stator (3) towards the rotor (4), wherein the gap tube (10) is produced inside the housing (2) from a preform (11) made of a thermoplastic material by a stretch blow-moulding process or extrusion blow-moulding process according to one of claims 1 to 10, and that, in axial direction between the stator (3), in particular its laminated core (16), and a housing cover (5.1, 5.2), a supporting device (9) for the gap tube (10) is provided.

11. Electric motor according to claim 10, characterized in that at least one housing cover (5.1, 5.2) is provided at at least one axial end of the electric motor (1).

12. Electric motor according to one of claims 10 or 11, characterized in that the gap tube (10) is bonded to the supporting device (9) and / or the stator (3).

13. Electric motor according to one of claims 11 or 12, characterized in that a separate seal (19) is provided between a housing cover (5.1, 5.2) and the gap tube (10).

14. Electric motor according to one of claims 10 to 13, characterized in that the wall thickness of the gap tube (10) is 0.05 to 0.5 mm.

15. Electric motor according to one of claims 10 to 14, characterized in that the gap tube (10) has a constant wall thickness over its length.

16. Electric motor according to one of claims 10 to 15, characterized in that the gap tube (10) consists of at least two layers.