Rotor for an electric machine

Abstract

The invention relates to a protective sleeve (12) for a rotor (1, 100) for an electric machine, in particular for a gas supply device for supplying air to a fuel cell stack, having at least one magnetic body (13) that is arranged between a first shaft body (10) and a second shaft body (11) of the rotor in an axial direction (2), wherein the first shaft body (10), the magnetic body (13) and the second shaft body (11) are arranged in succession in the axial direction of the rotor, wherein the at least one magnetic body (13) has end faces (21, 22) that are arranged in succession in the axial direction (2), wherein the first end face (21) is oriented facing the first shaft body (10) and the second end face (22) is oriented facing the second shaft body (11), wherein the protective sleeve (12) is configured to support the magnetic body (13) and to protect it from environmental influences, wherein, for this purpose, the protective sleeve (12) is configured to surround the magnetic body (13) in the axial direction, characterized in that the protective sleeve is made from a nitrogen-alloyed austenitic steel.

Description

[0001] Description

[0002] title

[0003] Rotor for an electric machine

[0004] State of the art

[0005] The invention is based on a protective sleeve for a rotor according to the preamble of the independent claim.

[0006] A bandage for such a rotor is already known from DE 10 2021 207399 A1.

[0007] WO 2006 / 043734 A1 discloses the use of Inconel in the manufacture of an air compressor rotor. The disadvantage here is that the base material costs are higher than they would be if steel were used.

[0008] Disclosure of the invention

[0009] The protective sleeve, manufactured according to the invention from a nitrogen-alloyed, austenitic steel, advantageously ensures optimized protection for a magnetic body of a rotor of an electrical machine. The protective sleeve is designed to support the magnetic body or to protect it from environmental influences, with the protective sleeve surrounding the magnetic body in the axial direction for this purpose. In particular, the protective sleeve is advantageously suitable for a high-speed air compressor for fuel cells for supplying the cathode side of the fuel cells with oxygen.

[0010] By replacing a nickel-based alloy Inconel, which is used for similar purposes, with a nitrogen-alloyed, austenitic steel alloy with low permeability, costs are reduced and a magnetic short circuit of the magnet via the sleeve is prevented. This also advantageously ensures the achievable magnetic moment and the associated functionality of a rotor of an electrical machine.

[0011] The measures listed in the dependent claims enable advantageous further developments and improvements of the protective sleeve specified in the independent claim.

[0012] Advantageously, the nitrogen-alloyed, austenitic steel is alloyed in such a way that the magnetic permeability is very low, in particular, less than 1.005. With a magnetic permeability of less than 1.005, a magnetic short circuit between the sleeve and the encased magnetic body is reliably prevented in the rotor of an electrical machine.

[0013] If the nitrogen content is selected in a range between 0.5 and 1.3 weight percent, the desired low permeability can be achieved while maintaining strength. The strength, expressed by the proportional limit Rp0.2 of the steel's elasticity, is advantageously up to approximately 2000 MPa, depending on the nitrogen content, with a manageable degree of cold forming. Brief description of the drawings

[0014] Embodiments of the invention are illustrated in the drawing and explained in more detail in the following description

[0015] It shows

[0016] Figure 1 shows a section of a rotor with a protective sleeve and

[0017] Figure 2 shows a section of an alternative rotor with a protective sleeve.

[0018] Embodiments of the invention

[0019] Figure 1 shows a substantially central section of a rotor 1 for an electrical machine, in particular for a gas supply device or an electric air compressor for supplying air to a fuel cell stack, with a magnetic body 13 which is arranged in an axial direction 2 between a first (10) and a second shaft body 11 of the rotor. The first shaft body 10, the magnetic body 13 and the second shaft body 11 are arranged one behind the other in the axial direction of the rotor, wherein the at least one magnetic body 13 has end faces 21, 22 arranged one behind the other in the axial direction 2. The first end face 21 is aligned with the first shaft body 10 and the second end face 22 with the second shaft body 11.

[0020] Each of the end faces 21, 22 lies partially directly on the adjacent shaft body 10, 11.

[0021] The magnetic body 13 is surrounded by a sleeve 12 for support and protection against environmental influences. When the electric machine is designed as an electric air compressor for fuel cell applications, a compressor impeller for the air to be compressed and / or a turbine wheel for energy recovery from flowing exhaust gas from the fuel cell stack are arranged on the shaft bodies to the left and right of the magnetic body in a manner not shown in detail.

[0022] The shaft bodies 10, 11 are preferably made of a metallic material. The sleeve 12 is made of a non-magnetic, preferably metallic material.

[0023] In detail, the shaft bodies 10, 11 each have, on their side facing the magnetic body 13, a region 24 or 25 with a stepped geometry such that the end faces 21, 22 of the magnetic body only partially rest on the adjacent shaft body 10 or 11. The stepped geometries are rotationally symmetrical to the axial direction 2 and each have a cylindrical wall-shaped projection 27 or 28, with a cylindrical end face 30 or 31 of the respective projection resting directly on the magnetic body 13.

[0024] Furthermore, the stepped geometries 24, 25 each comprise an outer circumferential step 33 or 34 such that the sleeve 12 can rest flush on the shaft bodies at its ends facing the shaft bodies 10, 11, so that the section of the rotor 1 shown in Figure 1 has a continuous cylindrical surface.

[0025] Such a rotor can be produced in a manufacturing process in which the two shaft bodies 10, 11 and the magnetic body 13 are thermally joined in a single process step or in separate process steps, for example, by a material-to-material bond. The joining preferably takes place with the support or protective sleeve 12 included.

[0026] Figure 2 shows a substantially central section of an alternative rotor 100 for an electrical machine, in which identical or similar components as in Figure 1 are provided with the same reference numerals and will not be described again. In contrast to rotor 1, in the alternative rotor 100, a preferably non-magnetic metallic cover plate 40 is located between the shaft bodies 10, 11 and the magnetic body 13, so that the end faces 21, 22 of the magnetic body rest on the respective cover plate, while the cover plates, in turn, rest on the cylinder end faces 30, 31 on the side facing away from the magnetic body.

[0027] In both designs, the material for the protective sleeve is a high-nitrogen austenitic steel, particularly one with very low magnetic permeability. For example, the magnetic permeability is less than 1.005.

[0028] In addition to iron, the nitrogen-alloyed, austenitic steel preferably contains the following alloy components:

[0029] Nitrogen in a range between 0.5 and 1.3 weight percent, carbon in a range between 0.01 and 0.2 weight percent, chromium in a range between 10 and 30 weight percent, manganese in a range between 4 and 20 weight percent,

[0030] Molybdenum in a range between 2 and 8 percent by weight,

[0031] Nickel in a range between 0 and 22 percent by weight and

[0032] Silicon in a range between 0 and 1.3 percent by weight.

[0033] The above-mentioned combination of alloy components ensures a very low permeability of less than 1.005 while maintaining the strength of the material.

[0034] In a method for producing a protective sleeve, a nitrogen-alloyed, austenitic steel is used, preferably comprising the above-mentioned alloy proportions of nitrogen, carbon, chromium, manganese, molybdenum, nickel and silicon.

Claims

Claims 1 . Protective sleeve (12) for - a rotor (1, 100) for an electrical machine, in particular for a gas supply device for supplying air to a fuel cell stack, having at least one magnetic body (13) which is arranged in an axial direction (2) between a first (10) and a second shaft body (11) of the rotor, wherein the first shaft body (10), the magnetic body (13), and the second shaft body (11) are arranged one behind the other in the axial direction of the rotor, wherein the at least one magnetic body (13) has end faces (21, 22) arranged one behind the other in the axial direction (2), wherein the first end face (21) is aligned with the first shaft body (10) and the second end face (22) is aligned with the second shaft body (11), - wherein the protective sleeve (12) is designed to support the magnetic body (13) or to protect it from environmental influences, - wherein the protective sleeve (12) is arranged for this purpose to surround the magnetic body (13) in the axial direction, characterized in that the protective sleeve is made of a nitrogen-alloyed, austenitic steel.

2. Protective sleeve according to claim 1, characterized in that the nitrogen-alloyed, austenitic steel has a very low magnetic permeability.

3. Protective sleeve according to claim 2, characterized in that the magnetic permeability is less than 1.

005.

4. Protective sleeve according to one of the preceding claims, characterized in that in the nitrogen-alloyed, austenitic steel, the alloying proportion of nitrogen is in a range between 0.5 and 1.3 percent by weight.

5. Protective sleeve according to any one of the preceding claims, characterized in that the nitrogen-alloyed, austenitic steel contains carbon and that the alloying proportion of carbon is in a range between 0.01 and 0.2 percent by weight.

6. Protective sleeve according to one of the preceding claims, characterized in that the nitrogen-alloyed, austenitic steel contains chromium and that the alloying proportion of chromium is in a range between 10 and 30 percent by weight.

7. Protective sleeve according to one of the preceding claims, characterized in that the nitrogen-alloyed, austenitic steel contains manganese and that the alloying proportion of manganese is in a range between 4 and 20 percent by weight.

8. Protective sleeve according to one of the preceding claims, characterized in that the nitrogen-alloyed, austenitic steel contains molybdenum and that the alloying proportion of molybdenum is in a range between 2 and 8 percent by weight.

9. Protective sleeve according to one of the preceding claims, characterized in that the nitrogen-alloyed, austenitic steel contains nickel and that the alloying proportion of nickel is in a range between 0 and 22 percent by weight.

10. Protective sleeve according to one of the preceding claims, characterized in that the nitrogen-alloyed, austenitic steel contains silicon and that the alloying proportion of the silicon is in a range between 0 and 1.3 percent by weight.

11. A method for producing a protective sleeve according to any one of the preceding claims, characterized in that it is formed from a nitrogen-alloyed, austenitic steel.

12. Rotor (1, 100) for an electrical machine, in particular for a gas supply device for supplying air to a fuel cell stack, with at least one magnetic body (13) which is arranged in an axial direction (2) between a first (10) and a second shaft body (11) of the rotor, wherein the first Shaft body (10), the magnetic body (13) and the second shaft body (11) are arranged one behind the other in the axial direction of the rotor, wherein the at least one magnetic body (13) has end faces (21, 22) arranged one behind the other in the axial direction (2), wherein the first end face (21) is aligned with the first shaft body (10) and the second end face (22) is aligned with the second shaft body (11), with a protective sleeve (12) surrounding the magnetic body (13) according to one of claims 1 to 10.

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