Method for manufacturing a combined axle, combined axle, electric motor and vehicle

Abstract

A method of manufacturing a composite shaft includes the steps of expanding an inner diameter of at least one joint portion of a first shaft member and / or reducing an outer diameter of at least one joint portion of a second shaft member, positioning the joint portion of the first shaft member around the joint portion of the second shaft member, welding the first shaft member and the second shaft member by forcing a current through the first shaft member and the second shaft member, and reducing the inner diameter of at least the joint portion of the first shaft member and / or increasing the outer diameter of at least the joint portion of the second shaft member.

Description

Technical Field

[0001] The present invention relates to a combined shaft, and more particularly to a shaft-hub connection for various applications, using a hollow shaft instead of a solid shaft, and the hollow shaft can be installed in an electric motor (e.g., an electric motor in an electric vehicle) as a load-bearing shaft for a rotor assembly. Background Technology

[0002] The rotor shaft comprises various sections characterized by different requirements. These requirements arise on the one hand from the end sections, which are typically designed as bearing points and are therefore usually heat-treated and ground or machined; and on the other hand from the central section, to which the rotor assembly is applied by various methods. The rotor assembly can be pressed onto a very precise and typically ground shaft. Advantageously, this central section is hollow or contains holes through which cooling medium can flow, which can cool the rotor assembly during operation. The end pieces at each end of the shaft may have teeth or other form-locking elements, which may be hardened or soft, to transmit or return the torque generated by the rotation of the rotor assembly in the stator to the gearbox or other connected components.

[0003] Depending on the load, the various components of the combined shaft are subjected to stress to varying degrees. Specifically, the side directly acting on the gearbox is characterized by both static and dynamic torque, which acts on the shaft-hub connections of the various components of the rotor shaft.

[0004] The misalignment between the various acting elements and the geometric misalignment caused by the bearings on both sides results in bending stress, which can also be described as rotational bending stress. These are speed-dependent in terms of the number of load reversals and load cycles, and are equivalent in magnitude to the geometric misalignment and the nominal load height for individual load times.

[0005] The advantages of a composite rotor shaft composed of shaft elements are obvious. Firstly, the individual shaft elements of the composite shaft can be optimized in terms of weight and load, and can be designed from the smallest possible hollow body. Therefore, weight reduction is achievable. Because the individual shaft elements are relatively small, simpler and more cost-effective production processes can be implemented in mass production using forming processes such as cold extrusion, semi-hot extrusion, or hot extrusion. The material composition of each shaft element can be selected based on stress; that is, high-quality, high-alloy materials can be selected for bearing points, while lower-quality materials can be used for other areas with lower mechanical stress.

[0006] Furthermore, the input weight for heat treatment or other processing of shaft components is significantly lower than that for the entire shaft, resulting in more cost-effective fixed quality and manufacturing equipment.

[0007] It is known to construct a camshaft from several hollow bodies by capacitor discharge welding. It is also known to construct a turbocharger by capacitor discharge welding of a hollow shaft to a turbine disc, wherein the turbine disc also contains a hollow cross-section.

[0008] DE102014202929A1 discloses a wheel bearing hub and a flange, which are connected to each other by pulse welding in a material-to-material bonding manner.

[0009] EP372663B1 discloses pressure welding of rotationally symmetric metallic bodies onto a metal shaft. Capacitive discharge welding can be used as a method for pressure welding.

[0010] WO2009 / 052885 discloses a method for connecting the turbine rotor and the shaft of the exhaust gas turbocharger by capacitor discharge welding.

[0011] Existing technologies do not provide techniques for manufacturing combined shafts that meet the requirements of electric vehicles. Summary of the Invention

[0012] One object of the present invention is to provide a combined shaft and a method for manufacturing the combined shaft, wherein the combined shaft can meet the requirements of electric motors (especially electric motors for electric vehicles).

[0013] The above-mentioned objective of the present invention is achieved by the method for manufacturing the combined shaft and the combined shaft as described below.

[0014] This invention discloses a method for manufacturing a composite shaft, comprising the steps of enlarging the inner diameter of at least one engagement portion of a first shaft element and / or reducing the outer diameter of at least one engagement portion of a second shaft element. The method includes the step of positioning the engagement portion of the first shaft element around the engagement portion of the second shaft element. The method further includes the step of welding the first shaft element and the second shaft element by forcing an electric current through the first shaft element and the second shaft element.

[0015] The method includes the steps of reducing the inner diameter of at least the engagement portion of the first shaft element and / or increasing the outer diameter of at least the engagement portion of the second shaft element.

[0016] Therefore, the first shaft element and the second shaft element are crimped and welded. It should be understood that a composite shaft may include more than two shaft elements that engage with each other to form the composite shaft.

[0017] The method may include the step of disposing a resilient element between the engagement portion of the first shaft element and the engagement portion of the second shaft element. The resilient element may act as a centering element to center the first shaft element relative to the second shaft element prior to the step of welding the first shaft element and the second shaft element. The method may further include the steps of forming a surrounding groove in the second shaft element and positioning the resilient element in the surrounding groove. The resilient element may protrude from the surrounding groove.

[0018] The elastic element can be made of plastics, polyetheretherketone polymers, polyethylene, rubber-like materials, non-ferrous metals, low-alloy metals, etc.

[0019] The aforementioned press-fit and welding techniques can meet high load requirements at a low cost. The welded joint of the first and second shaft elements is preferably achieved through capacitor discharge welding, resulting in a low-cost, high-quality welded joint, and then reinforced with pressfit. This allows the joint to absorb not only static and dynamic torsional forces, but also alternating static and dynamic bending stresses and circumferential bending stresses. Compared to the commonly used laser welding method, this significantly reduces costs, as laser welding is very expensive and does not exhibit the same behavior under continuous loads.

[0020] When designing shaft-hub connections, it is crucial to have the ability to determine the scale of an explicit solution for the load spectrum required by the application. Welds can be designed radially with multiple protrusions, allowing even very high torques exceeding 1000 Nm to be applied. Furthermore, by press-fitting, the scale can be correspondingly determined axially for various bending stresses exceeding 300 Nm, ensuring no negative impact on the shaft-hub connection throughout its service life. This ensures the robustness of the entire system, and press-fitting can be used in a wide range of applications.

[0021] The method may further include the step of forming a protrusion on the first shaft element pointing toward the second shaft element. Additionally or alternatively, the method may include the step of forming a protrusion on the second shaft element pointing toward the first shaft element. The method then includes the step of welding the first shaft element and the second shaft element by melting the protrusion with an electric current. The protrusion creates a low-resistance region in which the current flows. The protrusion melts and seals the gap between the mating portion of the first shaft element and the mating portion of the second shaft element to prevent corrosion and to create a mechanically strong connection.

[0022] The method further includes the step of forming the protrusion axially from the axial end face of the second shaft element toward the axial end face of the first shaft element.

[0023] The step of forming a protrusion on the first shaft element pointing towards the second shaft element and / or the step of forming a protrusion on the second shaft element pointing towards the first shaft element includes the step of forming a tapered protrusion. The tapered protrusion generates a high current density to melt the tapered protrusion and rapidly weld the first shaft element and the second shaft element. Multiple protrusions may be disposed on the axial end face of the second shaft element, wherein these protrusions are positioned at a fixed radius centered on the axis of the second shaft element. These protrusions melt during welding (e.g., capacitor discharge welding).

[0024] During capacitor discharge welding (CDM), accurate positioning of the components to be welded is crucial, as any deviation or eccentricity will lead to imbalance of the finished rotor shaft and increase machining or cutting workload. Therefore, during CDM, auxiliary devices should be used to center the parts to be joined in the best possible way, ideally by less than approximately 0.1 mm. These protrusions are then melted, so that the current discharges precisely at the point of lowest resistance and where contact is formed between the two joining parts within the very short duration of CDM. As the current discharge causes localized heating of the weld protrusion, the material in that area melts within milliseconds. In CDM, a permanently constant contact force acts axially on these shaft elements in a superimposed manner, thus forming a weld joint in the shortest possible time during the melting process. This occurs without heating the parts to be welded, because the welding process spans a very short period.

[0025] However, outside the welding area, contact between these mating parts must be prevented.

[0026] The pressing process requires very small tolerances between the mating parts being pressed (i.e., the mating portion of the first shaft element and the mating portion of the second shaft element). Pressing is forced through mechanical contact. This results in a defined overlap between the mating portions of the first and second shaft elements that are joined to form the press. Depending on the dimensions and materials used, the press is designed to withstand applied loads.

[0027] To combine these two processes, a conventional preferred axial capacitor discharge welding joint is first performed.

[0028] The engagement portion of the first shaft element can be enlarged so that the engagement portion of the first shaft element and the engagement portion of the second shaft element can enter each other with a minimum radial clearance (less than 0.3 mm).

[0029] Enlargement can be achieved through various methods (on the one hand, through the action of heat or other media, and on the other hand, through mechanical, electromechanical, or hydraulic action). In one embodiment, induction heating of the engagement portion of the first shaft element causes an increase in the inner diameter of the engagement portion.

[0030] Furthermore, the effective diameter of the engagement portion of the second shaft element can be reduced. This can be achieved by supplying a cooling medium (e.g., liquid nitrogen) or by mechanical, electromechanical, or hydraulic methods that result in a reduction in diameter, for example, but not only by axial elongation, provided that this is within the elastic limits of the material and the diameter relaxes to its original size upon subsequent release.

[0031] In both cases, capacitor discharge welding can be performed on the contact planes of the two joints because the parts do not contact each other radially during welding. However, to properly determine the gap size to meet load requirements rather than the jointing method, an additional elastic element and a jointing aid can be used respectively.

[0032] The elastic element (joining aid) can be made of material placed in a groove formed within one of the two mating members (the joining portion of the first or second shaft element). During engagement, the elastic element spacees the two joining portions axially apart, thus preventing direct electrical contact and therefore any flow of electrical energy. During the pressing process, i.e., when the two mating members (the joining portions of the first and second shaft elements) are pressed together, the elastic element (joining aid) can retract into the corresponding groove. Therefore, the groove is larger in volume than the elastic element. The elastic joining aid (elastic element) can deform such that it utilizes the available volume of the annular groove. The elastic joining aid can also have an additional fine centering effect, depending on its rigidity. This ultimately means that the imbalance caused by the shaft-hub connection is significantly lower than that of a conventional capacitor welding connection.

[0033] For example, if the rotor shaft (in one embodiment, the first shaft element) is heated, the heat generated will radiate to the welded portion and cause the welded portion to cool more slowly, thereby reducing the formation of cracks and, in the best case, eliminating cracks completely.

[0034] If this heating and expansion are carried out simultaneously, energy optimization can be achieved in several ways. For example, the waste heat from the hardened first shaft element can be used to expand the second shaft element, and the waste heat during the final cooling process has a tempering function for the next batch.

[0035] If the connection between the first and second shaft elements is designed to allow molten material to flow into free space, an airtight connection is created. This airtight connection seals the required area, such as the joint between the first and second shaft elements, according to the design. This sealing function ensures reduction or complete elimination of crevice corrosion, which is always a potential threat. In this respect, a significant increase in the overall service life of the press-welded joint is ensured.

[0036] The method further includes the step of forming a generally cylindrical opening extending axially toward the end face of the first shaft element, wherein the generally cylindrical opening in the end face of the first shaft element constitutes the engagement portion of the first shaft element. The method further includes the step of positioning the engagement portion of the second shaft element within the generally cylindrical opening in the end face of the first shaft element.

[0037] The step of increasing the inner diameter of at least the joint portion of the first shaft element includes heating at least the joint portion of the first shaft element. This prevents breakage that occurs after capacitor discharge soldering. The method further includes a step of decreasing the inner diameter of at least the joint portion of the first shaft element, which includes cooling the joint portion of the first shaft element. This cooling is not necessarily performed using a cooling medium. The cooling step can be performed by any type of forced or unforced cooling.

[0038] In one embodiment, the first shaft element and / or the second shaft element may be a hollow shaft. Therefore, coolant can flow through a hollow shaft cooling element positioned on the hollow shaft.

[0039] The method may further include the step of mounting a rotor of an electric motor on the first shaft element and / or the second shaft element. The rotor assembly can be cooled if coolant flows through a hollow shaft.

[0040] The step of welding the first shaft element and the second shaft element by forcing an electric current through them includes capacitor discharge welding. During this step, the first shaft element and the second shaft element are pressed against each other.

[0041] The present invention further discloses a composite shaft manufactured by the above-described method steps.

[0042] The present invention further discloses a composite shaft comprising a first shaft element having a engagement portion having an inner diameter. A second shaft element of the composite shaft has an engagement portion having an outer diameter, wherein the engagement portion of the first shaft element is press-fitted around the engagement portion of the second shaft element. The front side of the engagement portion of the second shaft element is welded to the first shaft element.

[0043] The combined shaft can be configured as described above.

[0044] As described above, the elastic element is disposed between the engagement portion of the first shaft element and the engagement portion of the second shaft element.

[0045] The present invention also discloses an electric motor comprising or including a combined shaft manufactured according to the above method steps. In this embodiment, a rotor element may be disposed on the first shaft element and / or the second shaft element.

[0046] The present invention further discloses a vehicle comprising a combined shaft manufactured according to the above method steps or an electric motor having a combined shaft manufactured according to the above method steps. Attached Figure Description

[0047] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0048] Figure 1 A cross-sectional view showing the engagement of the first shaft element and the second shaft element;

[0049] Figure 2 show Figure 1 The amplified portion;

[0050] Figure 3a Displays a composite shaft manufactured from three shaft elements;

[0051] Figure 3b Displays a composite shaft manufactured from three shaft elements;

[0052] Figure 4 A portion of the second shaft element is shown, in which a groove for accommodating an elastic element is formed;

[0053] Figure 5 The first and second shaft elements are shown before welding;

[0054] Figure 6 A partial sectional view of the first shaft element and the second shaft element is shown after the first shaft element has been welded and pressed onto the second shaft element.

[0055] Explanation of reference numerals in the attached figures

[0056] 100. Combined shaft;

[0057] 102. First shaft element;

[0058] 104. Second shaft element;

[0059] 106. Protrusion;

[0060] 108. Cylindrical opening;

[0061] 110. Groove;

[0062] 112. Elastic element;

[0063] 112a. Elastic element;

[0064] 112b. Elastic element;

[0065] 114. Figure 1 Part of;

[0066] 116. Cone;

[0067] 118. Joint;

[0068] 120. Joint portion;

[0069] 122. Axial end face;

[0070] 124. Axial end face;

[0071] 200. Combined shaft;

[0072] 202. Shaft elements;

[0073] 204. Shaft elements;

[0074] 206. Shaft elements;

[0075] 208. Rotor;

[0076] 300, combined shaft;

[0077] 302. Shaft elements;

[0078] 304. Shaft elements;

[0079] 306. Shaft elements;

[0080] 308. Rotor. Detailed Implementation

[0081] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0082] Figure 1Showing a cross-sectional view of a portion of a combined shaft 100 including a first shaft element 102 and a second shaft element 104. The first shaft element 102 and the second shaft element 104 are substantially cylindrical. An engagement portion 118 of the second shaft element 104 is positioned within a cylindrical opening 108 formed in the first shaft element 102. The cylindrical opening 108 extends substantially axially. An engagement portion 120 of the first shaft element 102 extends axially along the opening 108 in the first shaft element 102 and radially and axially fixes the engagement portion 118 of the second shaft element 104. In other words, the engagement portion 120 of the first shaft element 102 and the engagement portion 118 of the second shaft element 104 extend axially.

[0083] Figure 2 Show in zoomed-in view Figure 1 Part 114. A protrusion, a cone 116, etc., are formed on the second shaft element 104. Figure 2 In the diagram, the cone 116 is schematically shown extending into the first shaft element. This is not the case after welding the first shaft element and the second shaft element 104. Before inserting the engagement portion 118 of the second shaft element 104 into the axial opening 108 and engagement portion 120 of the first shaft element, the inner diameter of the engagement portion 120 of the first shaft element 102 is heated to increase the inner diameter of the engagement portion 120 of the first shaft element 102. The second shaft element 104 is moved into the axial opening 108 until the cone 116 contacts the axial end face 122 of the first shaft element 102. Therefore, the axial end face 124 of the second shaft element 104 is spaced apart from the axial end face 122 of the first shaft element 102.

[0084] Next, the first shaft element 102 and the second shaft element 104 are pressed axially against each other, forcing current to flow through them. This current can be generated by discharging a capacitor. The current flows through the cone 116 and melts it, causing the molten material to seal the end face 122 of the first shaft element 102 and the end face 124 of the second shaft element 104, thus fixing the end face 122 of the first shaft element 102 to the end face 124 of the second shaft element 104. Then, the temperature of the joint portion 120 of the first shaft element 102 is lowered. Because the joint portion 120 and end face 122 of the first shaft element 102 have been heated before welding, the formation of cracks can be significantly reduced, even if not eliminated. After cooling the engagement portion 120 of the first shaft element, the first shaft element 102 and the second shaft element 104 are secured by welding at their respective end faces 122 and 124 and by pressing together through a protrusion 106 extending axially from the end face 122 of the first shaft element 102 against the engagement portion 118 of the second shaft element 104. Capacitor discharge welding is known to those skilled in the art and therefore need not be described in further detail herein.

[0085] refer to Figure 3a The diagram shows a combined shaft 200 with three shaft elements 202, 204, and 206. These shaft elements are fixed to each other by crimping and welding, as described herein. The first shaft element 202 is a hollow shaft. The second shaft element 204 and the third shaft element 206 are partially hollow. The rotor 208 of an electric motor can be fixed to the first shaft element 202. The second shaft element 204 and the third shaft element 206 can serve as hubs.

[0086] Figure 3b Another embodiment of a combined shaft 300 comprising three shaft elements 302, 304, and 306 is shown. A rotor 308 of an electric motor can be mounted on the first shaft element 302. The first shaft element 302 is hollow. The second shaft element 304 is partially hollow. The third shaft element 306 is solid. The first shaft element 302, the second shaft element 304, and the third shaft element 306 can be secured by crimping and welding as described herein. The second shaft element 304 and the third shaft element 306 can function as hubs. These shaft elements can be made of steel. Shaft elements bearing high loads can be made of high-alloy steel, tempered steel, or hardened steel, while shaft elements bearing lower loads can be made of low-alloy steel.

[0087] Figure 4 The engagement portion 118 of the second shaft element 104 is shown in a partial cross-sectional view. A peripheral groove 110 is formed in the second shaft element. The peripheral groove 110 extends radially toward and around the periphery of the second shaft element 104. An elastic element 112 is positioned within the groove 110.

[0088] refer to Figure 5 This is a partial cross-sectional view showing the cross-sections of the first shaft element 102 and the second shaft element 104 during the process of engaging the first shaft element 102 and the second shaft element 104. The protrusion 106 of the engagement portion 120 of the first shaft element 102 partially moves over the engagement portion 118 of the second shaft element 104, causing the elastic element 112b to be compressed while the elastic element 112a remains uncompressed. Because the protrusion 106 has a larger diameter than the engagement portion 118 of the second shaft element 104, and because the engagement portion 120 of the first shaft element 102 has been heated, the engagement portion 120 of the first shaft element 102 and the engagement portion 118 of the second shaft element 104 are slightly spaced apart. The elastic elements 112a and 112b are used to center and / or align the first shaft element 102 relative to the second shaft element 104.

[0089] Figure 6 A partial cross-sectional view showing the cross-sections of the first shaft element 102 and the second shaft element 104 after cooling the protrusion 106 of the engagement portion 120 of the first shaft element 102. (See attached image.) Figure 6As shown, the engagement portion 120 of the first shaft element 102 and the engagement portion 118 of the second shaft element 104 are adjacent to each other to form compression and compressive elastic elements 112a and 112b.

[0090] The elastic elements 112a and 112b can be made of plastics, polyetheretherketone polymers, polyethylene, rubber-like materials, non-ferrous metals, low-alloy metals, etc.

[0091] The aforementioned press-fit and welding techniques can meet high load requirements at a low cost. The welded joints of shaft components are preferably achieved through capacitor discharge welding, resulting in a low-cost, high-quality welded joint, further enhanced by press-fitting. This allows for the absorption of high static and dynamic torsional forces and alternating static and dynamic bending stresses, as well as circumferential bending stresses. Compared to commonly used laser welding methods, the present invention significantly reduces costs, as laser welding is very expensive and does not exhibit the same behavior under continuous loads.

[0092] The above description is merely a preferred embodiment of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A method for manufacturing a composite shaft, characterized in that, Includes the following steps: Enlarge the inner diameter of at least one engaging portion of a first shaft element and / or reduce the outer diameter of at least one engaging portion of a second shaft element; Position the engagement portion of the first shaft element around the engagement portion of the second shaft element; The first shaft element and the second shaft element are welded by forcing an electric current through them; the inner diameter of at least the joint portion of the first shaft element is reduced and / or the outer diameter of at least the joint portion of the second shaft element is increased; It further includes at least one of the following two steps: A protrusion pointing toward the second shaft element is formed on the first shaft element; A protrusion pointing towards the first shaft element is formed on the second shaft element, and Further steps include the following: The first shaft element and the second shaft element are welded by melting the protrusion with the current; The engagement portion of the first shaft element is press-fitted around the engagement portion of the second shaft element.

2. The method for manufacturing a composite shaft as described in claim 1, characterized in that, The method further includes distributing an elastic element between the engagement portion of the first shaft element and the engagement portion of the second shaft element.

3. The method for manufacturing a composite shaft as described in claim 2, characterized in that, Further steps include the following: A surrounding groove is formed in the second shaft element; the elastic element is positioned in the surrounding groove.

4. The method for manufacturing a composite shaft as described in claim 1, characterized in that, The method further includes the step of forming the protrusion axially from the axial end face of the second shaft element toward the axial end face of the first shaft element.

5. The method for manufacturing a composite shaft as described in claim 1, characterized in that, The step of forming a protrusion on the first shaft element pointing toward the second shaft element and / or forming a protrusion on the second shaft element pointing toward the first shaft element includes the step of forming a tapered protrusion.

6. The method for manufacturing a combined shaft as described in claim 1, characterized in that, Further steps include the following: A cylindrical opening extending axially toward the first shaft element is formed in the end face of the first shaft element, wherein the cylindrical opening in the end face of the first shaft element constitutes the engagement portion of the first shaft element; and The engaging portion of the second shaft element is positioned within the cylindrical opening in the end face of the first shaft element.

7. The method for manufacturing a composite shaft as described in claim 1, characterized in that, The step of enlarging at least the inner diameter of the engagement portion of the first shaft element includes the step of heating at least the engagement portion of the first shaft element; and The step of reducing the inner diameter of at least the engagement portion of the first shaft element includes the step of cooling at least the engagement portion of the first shaft element.

8. The method for manufacturing a combined shaft as described in any one of claims 1-7, characterized in that, At least one of the first shaft element and the second shaft element is a hollow shaft.

9. The method for manufacturing a combined shaft as described in any one of claims 1-7, characterized in that, The method further includes the step of configuring a rotor of an electric motor on at least one of the first shaft element and the second shaft element.

10. The method for manufacturing a composite shaft as claimed in any one of claims 1-7, characterized in that, The step of welding the first shaft element and the second shaft element by forcing a current to flow through the first shaft element and the second shaft element includes capacitor discharge welding.

11. A composite shaft, comprising: A first shaft element having a engagement portion having an inner diameter; A second shaft element having a engagement portion having an outer diameter; The engagement portion of the first shaft element is press-fitted around the engagement portion of the second shaft element; The characteristic feature is that the axial end face of the joint portion of the second shaft element is welded to the axial end face of the first shaft element by the method described in any one of claims 1-10.

12. The combined shaft as described in claim 11, characterized in that, An elastic element is disposed between the engagement portion of the first shaft element and the engagement portion of the second shaft element.

13. An electric motor comprising the combined shaft manufactured according to the method steps of claims 1 to 10, or comprising the combined shaft as described in claim 11 or 12, characterized in that, One of the rotors is disposed on at least one of the first shaft element and the second shaft element.

14. A vehicle, characterized in that, It has a combined shaft as described in claim 11 or 12 or an electric motor as described in claim 13.

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