Method for the heat treatment of pressed strands and method for producing an electric motor and method for producing a motor vehicle

Abstract

The present invention relates to a method for heat treatment of pressed stranded wire (3), wherein the heat treatment of pressed stranded wire is performed in a state conventionally installed in a component of an electric motor (E); to a method for manufacturing an electric motor (E) comprising at least one component having at least one pressed stranded wire (3), wherein the pressed stranded wire is heat treated according to the present invention; and to a method for manufacturing a motor vehicle (K) including an electric motor (E), wherein the electric motor is manufactured according to the present invention.

Description

Technical Field

[0001] The invention relates to a method for heat treatment of pressed strands (or shaped strands) according to the preamble of claim 1, a method for manufacturing an electric motor according to the preamble of claim 14, and a method for manufacturing a motor vehicle comprising an electric motor according to the preamble of claim 15. Background Art

[0002] Pressed stranded wires are stranded wires that are compacted and thus have a specific cross-sectional shape (mostly a rectangular cross-sectional shape), i.e. a bundle of twisted or untwisted metal wires. The metal wires are preferably copper wires or metal wires made of a copper alloy. The metal wires themselves or the pressed stranded wires are surrounded by an insulating material (e.g. varnish). Pressed stranded wires mostly have end-side cable connectors that serve as electrical and / or mechanical interfaces for the pressed stranded wires.

[0003] Litz wires can be used as split conductors in electric machines, in particular stators. Split conductors are conductor sections that are inserted or pulled into, for example, stator slots. The protruding ends of two litz wires can then be directly connected to form half coils.

[0004] During the production of the pressed stranded wire, the wire is deformed, in particular cold-deformed. Due to the deformation, negative effects occur, such as a reduction in the electrical conductivity, since the ohmic resistance increases due to cold hardening.

[0005] One remedy here is to heat treat the pressed strands before installation in the electric motor, for example in the form of a recrystallization anneal. The lattice structure that has been disturbed by the cold deformation can be partially or completely restored by annealing. This depends primarily on the annealing temperature and duration. During the recrystallization annealing, the crystal structure is completely reformed; this is optimal for electrical conductivity.

[0006] Such a method is known, for example, from EP 30 96 440 A. However, the disadvantage of this method is the relatively high process complexity. The pressed strands are clamped in a holder and heated by an electric current. It is understood that this process is relatively expensive for the mass production of electric motors that are to be equipped with such pressed strands. Summary of the invention

[0007] The present invention is based on this and has the object of specifying an improved method for producing an electric motor, in particular a method which enables a more efficient heat treatment of the pressed strands.

[0008] According to the present invention, this object is achieved in that the pressed stranded wire is subjected to heat treatment in a state in which it is conventionally installed in a component of an electric motor. In other words, the pressed stranded wire is subjected to heat treatment in a state in which it is already installed and connected, rather than in an external device. As a result, no separate equipment is required. Furthermore, the heat treatment performed in the installed state of the pressed stranded wire is also advantageous, because the pressed stranded wires are no longer independent of each other, but are subjected to heat treatment together in the target system. In this regard, the installed pressed stranded wires can already interact with each other, thereby better compensating for the mutual influence of the pressed stranded wires with each other. The result is a pressed stranded wire system with less difference between the individual segmented conductors. The overall efficiency of the system is improved. The temperature hot spots are reduced qualitatively and quantitatively.

[0009] In particular, further advantageous embodiments of the proposed invention emerge from the features of the dependent claims. The subjects or features of the different claims can in principle be combined with one another as desired.

[0010] In an advantageous embodiment of the method, it can be provided that a heat treatment is performed after completion of the components, in particular the stator, after completion of the electric motor and before installation of the electric motor in a vehicle, and / or after or during commissioning of a vehicle comprising the electric motor.

[0011] In a further advantageous embodiment of the method, it can be provided that the heat treatment is a recrystallization annealing or a stress relief annealing.

[0012] In a further advantageous embodiment of the method, it can be provided that the component of the electric motor is a stator and / or a rotor of the electric motor. Preferably, the pressed strands are introduced into the stator, in particular as split conductors.

[0013] In another advantageous design of the method, it can be provided that the heating of the pressed stranded wire is carried out by applying an electric current to the pressed stranded wire for heat treatment. This way of introducing heat for heat treatment of the pressed stranded wire has many advantages. For example, the current flowing through the system precisely heats the parts with higher resistance more strongly. As a result, the defects of the pressed stranded wire system are precisely acted on for a longer time and / or at a higher temperature, and the heat treatment is thus more successfully carried out. The heat treatment achieved by current feeding also has the advantage that the heat is generated inside the conductor without having to penetrate the insulating material from the outside. Therefore, the degree of heating of the insulating material is lower than that of the annealing furnace. In addition, the annealing temperature achieved by current feeding is freely selectable and varies greatly in time. Thus, different annealing temperature curves can be run without having to maintain expensive temperature channels with different temperature ranges in the process, such as in a production line including an annealing line. In addition, each motor winding can be fed with a separate current and thus heat treated: two different motors can experience two different heat treatment curves on the same "heat treatment table" - for example, a favorable annealing curve can be determined experimentally. A heat treatment curve is understood here to mean a specific time-temperature curve or current-time curve.

[0014] In another advantageous design of the method, it can be preset that the pressed stranded wire is equipped with an insulating material, wherein the heat treatment is performed at a temperature lower than, equal to or higher than the long-term heat resistance of the insulating material. As long as the metal wire or stranded wire is heat treated without an insulator, or the metal wire or stranded wire has only a small amount of heat-sensitive insulating material, the heat treatment temperature can be selected in a wide range. However, if the insulated pressed stranded wire or its insulated metal wire is heat treated, a conflict of objectives will arise between the "optimal" heat treatment temperature and the maintenance of the insulator. For this reason, the insulated conductor or stranded wire is usually not heat treated, or is only heat treated at an extremely low temperature (far below the recrystallization temperature). A longer heat treatment duration can partially compensate for the lower temperature, but it has only limited economic significance on the production line. The heat treatment process below the tolerance temperature of the insulating material protects the insulating material, but requires a longer heat treatment process. Alternatively, heat treatment can also be performed at a temperature higher than the heat resistance of the insulating material. By this operating step, the insulation material's resistance to short-term heat resistance is deliberately utilized, so that the heat treatment is carried out under conditions that are higher than the insulation material's long-term heat resistance. In the case of professional implementation, this does not necessarily lead to the destruction of the insulation material, but it can lead to a significantly shorter heat treatment period, which can further rationalize the manufacturing process. Of course, it is also conceivable to carry out the heat treatment at a temperature corresponding to the highest long-term resistance temperature of the insulation material.

[0015] Temperatures of 150-250° C., in particular 170±10° C., have proven to be particularly advantageous for heat treatment. At such temperatures, which are in the vicinity of the permanent heat resistance of the insulating material, heat treatment can be carried out over long periods of time without fear of premature degradation of the material due to high heat input.

[0016] For the duration of a single heat treatment, a period of 30 to 300 minutes has proven to be more favorable. This period is long enough to produce a uniform temperature distribution on all pressed strands, which can reduce lattice defects in the pressed strand metal wires. In addition, the longer the heat treatment time, the larger the confidence interval for predicting the effect of the heat treatment. Therefore, under the same total action time, the probability of failure can be predicted more accurately compared to more frequent but shorter heat treatments.

[0017] In a further advantageous embodiment of the proposed method, it can be provided that the cumulative heat treatment duration of the pressed strands does not exceed 10% of the operating time of the pressed strands. As a result, the temperature-related aging effects of the heat treatment on the insulating material can be kept controllably low. In particular, the probability of failure and other risks can be predicted.

[0018] In another advantageous embodiment of the method, it can be provided that the heat treatment of the pressed wires is carried out after the electric motor is completed and before installation in the vehicle, and that the heat treatment of the pressed wires is carried out at an excessively high temperature, i.e. at a temperature that is higher than the long-term resistance temperature of the insulating material. The advantage of this manufacturing variant is that it can lead to premature failure of the system, thereby avoiding the installation of error-prone products in the final product. Preferably, the heat treatment of the pressed wires in the production line (i.e. after the component is completed, or after the electric motor is completed and before installation in the vehicle) can be carried out in parallel with other quality tests, so that the duration of the manufacturing process is not or hardly prolonged due to the heat treatment of the pressed wires. For this purpose, a test run of the engine system is preferably carried out during the factory acceptance.

[0019] In another advantageous embodiment of the method, it can be provided that the heat treatment of the pressed strands is carried out after the vehicle is put into operation or during this process, and that the heating of the pressed strands is produced by regulating or switching off the engine cooling and / or by idling, in particular due to a leakage current applied in a targeted manner, wherein the leakage current generates heat but does not generate any torque. The aforementioned possibility is characterized in that it can be carried out in a simple manner in the electric motor or in the vehicle due to the use of already existing elements, such as engine cooling or engine management. Ultimately, these measures can also be carried out or initiated by the end user of the motor vehicle. However, it is of course also conceivable to automatically initiate the heat treatment, for example based on a resistance measurement or a preprogrammed time interval.

[0020] In order to rationalize the production process, it can be provided that the heat treatment is divided into sub-intervals and the first part is carried out before the vehicle is first put into operation and all other time intervals are carried out after the vehicle is put into operation. In this way, the cycle time in engine production can be reduced without a lasting loss of efficiency.

[0021] In another advantageous embodiment of the method, provision can be made for the heat treatment to be repeated regularly, in particular quarterly or annually, so that it can be ensured that any cold hardening in the pressed strands, which can occur, for example, due to externally applied vibrations, does not lead to a permanent deterioration in the efficiency of the pressed strands.

[0022] In another advantageous embodiment of the method, it can be provided that a pressed stranded wire with a degree of compaction of more than 80% is used. Due to the high degree of compaction, the heat conduction between the individual wires of the pressed stranded wire is higher than in the case of a lower degree of compaction. As a result, a more homogeneous temperature distribution occurs over the cross section of the pressed stranded wire, so that higher annealing temperatures can be operated. In particular, the inner individual wires or the wires of the pressed stranded wire core can be heated almost up to the maximum permissible temperature for burning of the individual wire insulation, but in the process the maximum permissible temperature of the individual wire insulation of the outermost wire is not exceeded. Overall, the annealing time can be shortened in this way. A further object of the present invention is to provide an improved method for manufacturing an electric motor, wherein the electric motor comprises at least one component having at least one pressed stranded wire, and in particular to provide a method that enables a more rational heat treatment of the pressed stranded wire.

[0023] According to the invention, this object is achieved by a method having the characterizing features of claim 14. By using the method for heat treatment of pressed strands for the production of electric motors, the advantages resulting from the heat treatment method can be made available for the production of electric motors as well.

[0024] Another object of the present invention is to propose an improved method for producing a motor vehicle comprising an electric motor, in particular a method which enables a more rational heat treatment of the pressed strands in the electric motor.

[0025] According to the invention, this object is achieved by a method having the characterizing features of claim 15. By using the method for heat treatment of pressed strands for the production of vehicles or electric motors of vehicles, the advantages resulting from the heat treatment method can be made available also for the production of electric motors or vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other features and advantages of the present invention will become clear from the following description of preferred embodiments with reference to the accompanying drawings, which schematically show:

[0027] Figure 1 A side view shows a pressed stranded wire provided for the heat treatment according to the invention;

[0028] Figure 2 The front view shows a pressed stranded wire provided for the heat treatment according to the invention;

[0029] Figure 3 The stator of the electric motor is shown in a side cross-sectional view, including pressed litz wires and winding ends;

[0030] Figure 4 The stator of the electric motor is shown in a front view, including pressed litz wires and connecting tabs;

[0031] Figure 5 An electric motor comprising a stator equipped with pressed litz wires is shown in a side cross-sectional view;

[0032] Figure 6 A motor vehicle comprising an electric motor equipped with pressed litz wire is shown. DETAILED DESCRIPTION

[0033] First reference Figure 1 .

[0034] The pressed stranded wire 3 mainly comprises a plurality of metal wires 311, in particular copper wires or metal wires made of a copper alloy. The metal wires 311 are usually twisted together into a metal wire bundle 31, and the twisted metal wire bundle 31 is also compacted, in particular compressed into a rectangular cross section. Moreover, the individual metal wires are preferably provided with an insulator, generally lacquer, and the metal wire bundle is preferably provided with an insulator 32. The pressed stranded wire mostly has an end-side sleeve 33, which serves as an electrical interface of the pressed stranded wire and in particular as its mechanical interface.

[0035] The electric motor E (in particular an asynchronous motor) mainly comprises a stator 1 and a rotor 2 as main components. Preferably, the components of the electric motor (preferably the stator, but the rotor is also conceivable) are equipped with at least one pressed stranded wire 3. The pressed stranded wire used is preferably designed as a rod-shaped segmented conductor. The pressed stranded wire is preferably installed in the component in a manner known to those skilled in the art. The pressed stranded wires can be connected to each other, for example, by means of connecting tabs 4. The components including one or more pressed stranded wires are assembled together with other components to form an electric motor E. The electric motor is in turn installed in a vehicle K, preferably a motor vehicle.

[0036] Heat treatment can be carried out at different stages of production, in particular:

[0037] a) After completing the components, especially the stator,

[0038] b) after the electric motor is completed and before the electric motor is installed in a vehicle, and / or

[0039] c) After or during the commissioning of a vehicle comprising an electric motor.

[0040] Heat treatment preferably refers to recrystallization annealing or stress relief annealing. Recrystallization annealing is understood to mean annealing after cold forming at a temperature within the recrystallization range without phase change. Stress relief annealing is understood to mean annealing after cold deformation at a temperature below the recrystallization temperature without phase change.

[0041] Preferably, the heat for the heat treatment of the pressed strands is introduced by current feeding the pressed strands, i.e. by applying current to the pressed strands to be heated. (The symbols with a zigzag line represent heat input.) In this process, individual pressed strands can be selectively heated, in particular, current can be applied in a targeted manner to individual loops of the pressed strands for heat treatment.

[0042] The quality of the heat treatment process depends mainly on factors such as temperature and time. With regard to temperature, it is worth noting that the pressed strands 3 are provided with insulating material 32, which is damaged from a certain temperature, so that the time of the heat treatment is important. The maximum permissible temperature is in principle limited by the insulating material.

[0043] The thermal resistance of insulating materials is usually divided into several classes according to DIN EN 60085. Classes F (up to 155°C) and H (up to 180°C) are common in electric motors. Operation at temperatures above this will not lead to immediate failure of the insulation, but the insulation properties will be (temporarily) reduced and the service life or aging resistance will be (permanently) reduced. In particular, this is acceptable to a certain extent in view of the product requirements, especially in the case of sufficiently precise knowledge of the temperature-dependent aging behavior of the insulating material.

[0044] Therefore, in one embodiment variant, annealing is carried out at a temperature above the insulation grade, wherein the cumulative annealing time during the service life does not exceed 10% of the use time. A temperature of 150-250° C., in particular 170±10° C., is aimed at. The typical time interval of the heat treatment is between 30 and 300 minutes.

[0045] Depending on the production stage at which the heat treatment is carried out, particular advantages may result.

[0046] Thus, for example, it can be provided that the heat treatment is carried out after the electric motor is finished and before it is installed in the vehicle, and that the heat treatment is carried out at an excessively high temperature. In this case, an excessively high temperature is a temperature that is higher than the temperature permitted by the insulation class. The advantage of this radical manufacturing variant is that it can lead to premature failure of the system, thus preventing error-prone products from being installed in the end product.

[0047] Preferably, the heat treatment of the pressed strands is carried out in parallel with other quality tests in the production line (i.e. after the component is finished, or after the electric motor is finished and before installation in the vehicle), so that the production process is not or hardly prolonged by the heat treatment of the pressed strands. For this purpose, a test run of the engine system is preferably carried out during the factory acceptance test.

[0048] As already mentioned, heat treatment of the pressed strands can also be carried out after the vehicle is put into operation or during this process. This is preferably achieved by active temperature management. In order to maintain a high temperature even in time intervals of low engine use, active temperature management can include the following measures: a) deliberately cooling the engine, running it at low load or even shutting it down, b) generating engine heat by no-load, for example due to leakage currents applied in a targeted manner, wherein these leakage currents generate heat but no torque. Preferably, the annealing process is repeated regularly (for example quarterly or annually) to detect the aging-related decrease in conductivity. Depending on the application, the current feed is advantageously selected so that torque just occurs or just does not occur (for example direct current does not generate any torque in asynchronous machines). The proposed method is particularly suitable for pressed strands with a compaction degree of more than 80%. The compaction degree refers to the ratio of the metal wire surface (copper wire and the insulating varnish surrounding it) to the minimum covering of the pressed strand (excluding the main insulation).

[0049] Features and details described in conjunction with the method naturally also apply to the device and vice versa, so that with regard to the present disclosure reference is always made to one another or to individual inventive aspects.

[0050] Reference numerals list

[0051] The following reference numerals are used in the drawings:

[0052] K Motor Vehicles

[0053] E-Motor

[0054] 1 Stator

[0055] 2 Rotors

[0056] 3 Pressed stranded wire

[0057] 4 Connecting tabs

[0058] 31 Metal wire harness

[0059] 32 Insulator

[0060] 33 Casing

[0061] 311 Metal wire.

Claims

1. A method for heat treatment of pressed stranded wire (3), characterized in that After the electric motor (E) has been installed in a vehicle (K) and after or during the commissioning of the vehicle (K), the pressed strands (3) are subjected to heat treatment in a conventional state in which they are installed in a component of the electric motor (E). The pressed strands (3) are heated by regulating or switching off engine cooling and / or by idling due to a specifically applied leakage current, wherein the leakage current generates heat but does not generate any torque.

2. The method according to claim 1, characterized in that Heat treatment refers to recrystallization annealing or stress relief annealing.

3. The method according to claim 1 or 2, characterized in that: The components of the electric motor (E) are the stator (1) and / or the rotor (2) of the electric motor.

4. The method according to claim 1 or 2, characterized in that: The pressed stranded wire (3) is provided with an insulating material (32), wherein the heat treatment is performed at a temperature lower than, equal to or higher than the heat resistance of the insulating material.

5. The method according to claim 1 or 2, characterized in that: The heat treatment is performed at a temperature of 150-250°C.

6. The method according to claim 1 or 2, characterized in that: The heat treatment is performed at a temperature of 170±10°C.

7. The method according to claim 1 or 2, characterized in that: A single heat treatment is carried out over a period of time ranging from 30 to 300 minutes.

8. The method according to claim 1 or 2, characterized in that: The cumulative heat treatment time does not exceed 10% of the operating time of the pressed stranded wire.

9. The method according to claim 1 or 2, characterized in that: The heat treatment is repeated periodically.

10. The method according to claim 1 or 2, characterized in that: The heat treatment is repeated quarterly or annually.

11. The method according to claim 1 or 2, characterized in that: A pressed stranded wire (3) having a compaction degree of more than 80% is used.

12. A method for producing an electric motor (E) comprising at least one component having at least one pressed stranded wire (3), characterized in that A method for heat treatment of pressed stranded wires (3) according to any one of claims 1 to 11.

13. A method for manufacturing a motor vehicle (K) comprising an electric motor (E), characterized in that A method for manufacturing an electric motor according to claim 12.

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