Method for producing a piston for a thermoacoustic heat pump

Abstract

The invention relates to a method (1) for producing a piston (2) having a core body (3) and at least one support (4). In the method (1), the core body (3) and the at least one support (4) are interconnected via an intermetallic aluminum finishing layer. The invention also relates to a piston (2) produced in the method (1) and to a thermoacoustic heat pump comprising the piston (2).

Description

[0001] October 29, 2025

[0002] 1

[0003] Method for manufacturing a piston for a thermoacoustic heat pump

[0004] The invention relates to a method for manufacturing a piston with a core body and at least one support for a thermoacoustic heat pump. The invention also relates to the piston manufactured in the method and the thermoacoustic heat pump with the piston.

[0005] In a thermoacoustic heat pump, a gas within a closed tube is set into vibration by two oscillating pistons, creating a standing wave. This generates pressure differentials within the gas, allowing heat to be transferred between them. The gas is heated in the high-pressure (compressed) zones and cooled in the low-pressure (expansion) zones. In this way, the gas acts as a refrigerant in the heat pump. The piston is driven electromagnetically by a drive unit. The piston consists of a core made of a magnetic or magnetizable material such as iron or steel and a carrier made of aluminum or an aluminum alloy. The core and carrier are typically bolted together. However, this bolt can be subject to dynamic failure.Furthermore, the piston must have sufficient thickness to allow the core body and the carrier to be screwed together, and is therefore limited in its design.

[0006] The object of the invention is therefore to provide an improved or at least alternative embodiment of a method of the generic type, in which the described disadvantages are overcome. The object of the invention is also to provide a piston produced by the method and a thermoacoustic heat pump incorporating the piston.

[0007] This problem is solved according to the invention by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims. 29.10.2025

[0008] 2

[0009] The method according to the invention is designed for manufacturing a piston for a thermoacoustic heat pump, wherein the piston comprises a core body and at least one support. The method includes steps a), b), and c), which are carried out successively in the aforementioned order. In step a), the core body is provided from a metallic material. In step b), the core body is immersed in a molten first Al-Si alloy to produce an intermetallic Alfining layer on the surface of the core body, consisting of the core body material and the first Al-Si alloy. In other words, in step b), the core body is pretreated using an Alfining process.In measure c), the at least one support is produced by overmolding the core body, at least partially, with a molten second Al-Si alloy on the non-solidified intermetallic Alfinier layer on the core body. This creates an intermetallic bond between the non-solidified intermetallic Alfinier layer on the core body and the second Al-Si alloy, and thus between the at least one support and the core body. In other words, in measure c), the core body pretreated in the Alfinier process is cast as an insert with the second Al-Si alloy.

[0010] In the inventive method, the piston is formed by means of a composite casting – all conventional known casting processes can be used here – via an intermetallic connection between the core body and the support. In other words, the core body and the at least one support in the piston are metallurgically bonded to one another via the intermetallic Alfinier layer. This allows the heat generated in the piston to be dissipated more effectively from the support to the core body, and the expansion of the core body and the support is more uniform, thereby reducing wear between the piston and a cylinder guiding the piston. The metallurgical bond between the core body and the support also eliminates the need for a screw connection between the core body and the support. This can reduce CO2 emissions, as the 29.10.2025

[0011] 3

[0012] The vertical integration, energy consumption, and material quantity required for manufacturing the piston, as well as for recycling the piston, can be reduced. Furthermore, the wall thickness and thus the weight of the piston can be reduced, which can lower the energy consumption of the thermoacoustic heat pump. In addition, the piston can be manufactured in several shapes that are not possible with a screw connection between the core body and the carrier. Eliminating the screw connection therefore allows for greater design freedom for the entire component.

[0013] All casting processes known to those skilled in the art, such as sand casting, centrifugal casting, die casting, or pressure die casting, as well as all known processes for manufacturing semi-finished products, such as drawn, rolled, or extruded steel tubes, are suitable for producing the core body. The core body does not necessarily require mechanical machining at the connecting diameter to the carrier material and can be cast in its raw state using the process described above. This reduced manufacturing depth also contributes to a reduction in CO2 emissions.

[0014] Following step c) in step d), the core and the at least one support can be cooled so that the piston is completed, in which the core and the at least one support are metallurgically bonded via the intermetallic Alfinier layer. In other words, the intermetallic Alfinier layer can be formed in the completed piston between the core and the at least one support, metallurgically bonding the core and the at least one support. The intermetallic Alfinier layer can be connected to the core and to the at least one support via intermetallic bonds.

[0015] Following measure c), the piston can be finished or reworked in measure e). In particular, the piston can undergo final mechanical machining. The piston manufactured using a composite casting process can be further processed, especially on October 29, 2025.

[0016] 4. One piece can be finished, thereby saving on manufacturing depth and CO2 emissions. Measure e) can be carried out particularly after measure d).

[0017] Following measure c) in measure f), the piston can be coated, at least partially, with a sliding coating. The sliding coating can be applied to an outer surface of the wall facing away from the interior and, if necessary, to an outer surface of the bottom facing away from the interior. The coating can be formed, for example, by graphitizing, phosphating, or a similar process. The sliding coating can, in particular, reduce the friction between the piston and a cylinder guiding the piston. Measure e) can, in particular, be carried out following measures d) and f).

[0018] In measure a), the core body can be made of iron, steel, or a magnetic or magnetizable material. In measure a), the core body can be provided as a body that is rotationally symmetric or n-fold rotationally symmetric with respect to a longitudinal center axis of the piston. This simplifies the manufacturing of the piston. The first Al-Si alloy used in measure b) and the second Al-Si alloy used in measure c) can differ, at least in their silicon content. For example, the first Al-Si alloy can have a silicon content of less than 20%. The silicon content of the at least one support can be between 5% and 30%. In principle, all aluminum alloys known in this family can be used.

[0019] The invention also relates to a piston for a thermoacoustic heat pump comprising a core body and at least one support. The piston is manufactured using the method described above. Accordingly, the piston can comprise the core body made of a metallic material and the at least one support made of a second Al-Si alloy. The core body and the at least one support can be metallurgically bonded to one another via the intermetallic Alfinier layer made of a first Al-Si alloy. The intermetallic Alfinier layer can be a 29.10.2025

[0020] 5. Form an intermetallic compound with the metallic material of the core body and with the second Al-Si alloy of the at least one support.

[0021] In one possible embodiment, the piston can have a base oriented perpendicular to its longitudinal axis and a wall circumferencing it at a distance from its longitudinal axis. The piston can have an interior space that is partially bounded to the outside by the wall and the base. In other words, the piston can be pot-shaped.

[0022] The piston can have a sliding coating on an outer surface of the wall facing away from the interior and, optionally, on an outer surface of the head facing away from the interior. This coating can be formed, for example, by graphitizing, phosphating, or a similar process. The sliding coating can, in particular, reduce friction between the piston and a cylinder guiding the piston. The sliding coating can be applied after the piston has been machined or directly onto the machined piston. In principle, any known coating used on pistons in internal combustion engines can be used as a sliding coating.

[0023] The core body can form at least the wall and / or at least the bottom in sections. The at least one support can also form at least the wall and / or at least the bottom in sections. In other words, the core body and the at least one support can be shaped to fit each other so that together they form the entire piston. The core body can form at least some sections of the piston alone or together with the at least one support, and / or the at least one support can form at least some sections of the piston alone or together with the core body. Several possible embodiments of the piston are conceivable.

[0024] The core body can have at least a section of an exterior wall facing away from the interior and / or at least a section of a 29.10.2025

[0025] 6. The core body can form an interior area of ​​the wall facing the interior. The core body can form at least a section of the floor facing away from the interior and / or at least a section of the floor facing the interior.

[0026] The at least one support can form, at least partially, an exterior wall facing away from the interior and / or, at least partially, an interior wall facing the interior. The at least one support can form, at least partially, an exterior floor facing away from the interior and / or, at least partially, an interior floor facing the interior.

[0027] The outer and inner surfaces of the wall can encircle the longitudinal axis of the piston at a distance and abut each other radially. The outer surface of the wall can extend radially inward from a radially outer surface, and the inner surface can extend radially outward from a radially inner surface. In other words, the outer surface can surround the inner surface. The outer and inner surfaces can form the entire wall. The outer surface and inner surface of the base can be oriented perpendicular to the longitudinal axis of the piston and abut each other axially. The inner surface of the base can be located axially between the inner and outer surfaces of the base. The outer and inner surfaces can form the entire base.Several advantageous bottom shapes, such as those used in combustion engines, can be employed.

[0028] The invention also relates to a thermoacoustic heat pump. The heat pump comprises a housing, at least one piston as described above, and at least one drive unit for driving the at least one piston. The at least one piston and the at least one drive unit are arranged in the housing to interact electromagnetically with each other. The piston is located on 29.10.2025

[0029] 7. The housing is enclosed by a cylinder. The cylinder can be manufactured using all known manufacturing processes. In addition, known coatings can be used here in conjunction with the sliding coating to reduce wear and energy consumption.

[0030] In connection with the present invention, the abbreviations "Al" for aluminum and "Si" for silicon are used. It is understood that the first Al-Si alloy and the second Al-Si alloy may contain other components besides aluminum and silicon. The terms "axial," "radial," and "circumferential" in connection with this invention always refer to a longitudinal central axis of the piston.

[0031] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the associated description of the figures based on the drawings.

[0032] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0033] Preferred embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components.

[0034] They show, schematically, each one

[0035] Fig. 1 shows a flowchart of a method according to the invention for manufacturing a piston according to the invention; 29.10.2025

[0036] 8

[0037] Fig. 2 shows a sectional view of the piston according to the invention in a first embodiment;

[0038] Fig. 3 shows a sectional view of the piston according to the invention in a second embodiment;

[0039] Fig. 4 shows a sectional view of the piston according to the invention in a third embodiment;

[0040] Fig. 5 shows a sectional view of the piston according to the invention in a fourth embodiment;

[0041] Fig. 6 shows a sectional view of the piston according to the invention in a fifth embodiment;

[0042] Fig. 7 shows a sectional view of the piston according to the invention in a sixth embodiment;

[0043] Fig. 8 shows a sectional view of the piston according to the invention in a seventh embodiment;

[0044] Fig. 9 shows a sectional view of the piston according to the invention in an eighth embodiment;

[0045] Fig. 10 shows a sectional view of the piston according to the invention in a ninth embodiment;

[0046] Fig. 11 shows a sectional view of the piston according to the invention in a tenth embodiment;

[0047] Fig. 12 shows a sectional view of the piston according to the invention in an eleventh embodiment. 29.10.2025

[0048] 9

[0049] Fig. 1 shows a flowchart of a method 1 according to the invention for manufacturing a piston 2 according to the invention. The piston 2 comprises, with reference to Figs. 2 to 12, a core body 3 and at least one support 4. With reference to Fig. 1, steps a), b), and c) are carried out sequentially in the method 1. First, in step a), the core body 3 is prepared. The core body 3 is made of a metallic material such as steel or iron. In step b), the core body 3 is placed in a molten first Al-Si alloy. An intermetallic Alfining layer is formed on the surface of the core body 3 from the material of the core body 3 and the first Al-Si alloy. In step c), the core body 3 is encased in a second Al-Si alloy on the non-solidified or molten intermetallic Alfining layer. This creates a barrier around the core body 3 orAt least one support 4 is produced on the core body 3. Since the intermetallic Alfinier layer on the core body 3 has not solidified or melted, an intermetallic bond is formed between the intermetallic Alfinier layer and the second Al-Si alloy. This results in the core body 3 and the at least one support 4 being metallurgically bonded to each other in the completed piston 2 via the intermetallic Alfinier layer. The first Al-Si alloy and the second Al-Si alloy can have identical or different silicon contents.

[0050] Furthermore, after measure c), further alternative measures d), e), and f) are carried out. In measure d), the core body 3 and the support 4 are cooled so that the piston 2 is completed. After measure d), in measure e), the piston 2 is mechanically finished or reworked. After measure e), in measure f), the piston 2 is coated, at least partially, with a sliding coating.

[0051] Fig. 2 shows a sectional view of the piston 2 according to the invention in a first embodiment. The piston 2 is manufactured using the method 1 described above. The piston 2 is cup-shaped and comprises a wall 5 and a base 6. The wall 5 surrounds a longitudinal center axis LMA of the piston. 29.10.2025

[0052] 10 and the base 6 are oriented perpendicular to the longitudinal center axis LMA. The wall 5 and the base 6 define an interior space 7 of the piston 2. In the first embodiment of the piston 2, the core body 3 and the support 4 are rotationally symmetrical with respect to the longitudinal center axis LMA. Furthermore, the core body 3 and the support 4 are cup-shaped, with the core body 3 arranged within the support 4. Thus, the core body 3 forms an interior region 5a of the wall 5 facing the interior space 7 and an interior region 6a of the base 6 facing the interior space 7. The support 4, on the other hand, forms an exterior region 5b of the wall 5 facing away from the interior space 7 and an exterior region 6b of the base 6 facing away from the interior space 7.

[0053] Fig. 3 shows a sectional view of the piston 2 according to the invention in a second embodiment. The piston 2 is manufactured using the method 1 described above. In the second embodiment of the piston 2, the core body 3 and the support 4 are rotationally symmetrical with respect to the longitudinal center axis LMA. The core body 3 is cup-shaped and the support 4 is hollow cylindrical, with the core body 3 arranged inside the support 4. The core body 3 forms the inner region 5a of the wall 5 and completely the base 6. The support 4 forms only the outer region 5b of the wall 5.

[0054] Fig. 4 shows a sectional view of the piston 2 according to the invention in a third embodiment. The piston 2 is manufactured using the method 1 described above. In the third embodiment of the piston 2, the core body 3 and the support 4 are rotationally symmetrical with respect to the longitudinal center axis LMA. The core body 3 is cup-shaped and the support 4 is disc-shaped. The support 4 is arranged on the outside of the core body 3 and forms the outer surface 6b of the base 6. The core body 3 completely forms the wall 5 and the inner surface 6a of the base 6.

[0055] Fig. 5 shows a sectional view of the piston 2 according to the invention in a fourth embodiment. The piston 2 is manufactured using the method 1 described above. In the fourth embodiment, the piston 2 has exactly two supports 4 - see also 29.10.2025

[0056] 11. For better distinction, these are designated as 4a and 4b. The two supports 4a and 4b are formed simultaneously in measure c) of procedure 1. The core body 3 and the supports 4a and 4b are rotationally symmetrical with respect to the longitudinal center axis LMA. The core body 3 is pot-shaped, the support 4a is hollow cylindrical, and the support 4b is disc-shaped. The support 4a is arranged inside the core body 3, and the support 4b is arranged on the outside of the core body 3. Here, the core body 3 forms the outer surface 5b of the wall 5 and the inner surface 6a of the base 6. The support 4a forms the inner surface 5a of the wall 5, and the support 4b forms the outer surface 6b of the base 6.

[0057] Fig. 6 shows a sectional view of the piston 2 according to the invention in a fifth embodiment. The piston 2 is manufactured using the method 1 described above. In the fifth embodiment of the piston 2, the core body 3 and the support 4 are rotationally symmetrical with respect to the longitudinal center axis LMA. Here, the core body 3 is hollow cylindrical and the support 4 is cup-shaped, with the core body 3 arranged inside the support 4. As a result, the core body 3 forms only the inner region 5a of the wall 5. The support 4 forms the outer region 5b of the wall 5 and the entire base 6.

[0058] Fig. 7 shows a sectional view of the piston 2 according to the invention in a sixth embodiment. The piston 2 is manufactured using the method 1 described above. In the sixth embodiment of the piston 2, the core body 3 and the support 4 are rotationally symmetrical with respect to the longitudinal center axis LMA. Here, the core body 3 is hollow cylindrical and the support 4 is cup-shaped. The support 4 forms the outer surface 5b of the wall 5 and the entire base 6. The core body 3 is axially shorter than the support 4 and forms the inner surface 5a of the wall 5 only in sections. The core body 3 is arranged axially spaced from the base 6 and extends to an axial edge 8 of the piston 2 facing away from the base 6. The inner surface 5a of the wall 5 is thus formed axially adjacent to the edge 8 by the core body 3 and axially adjacent to the base 6 by the support 4. The core body 3 is located on 29.10.2025

[0059] 12

[0060] Recess 9 of the support 4, so that the wall 5 facing the interior 7 is completely step-free or flat.

[0061] Fig. 8 shows a sectional view of the piston 2 according to the invention in a seventh embodiment. The piston 2 is manufactured using the method 1 described above. In the seventh embodiment of the piston 2, the core body 3 and the support 4 are rotationally symmetrical with respect to the longitudinal center axis LM A. Here, in contrast to the sixth embodiment, the core body 3 is axially spaced from the base 6 and the edge 8. The core body 3 also lies in the recess 9 of the support 4, so that the wall 5 facing the interior 7 is completely smooth and level.

[0062] Fig. 9 shows a sectional view of the piston 2 according to the invention in an eighth embodiment. The piston 2 is manufactured using the method 1 described above. In the eighth embodiment, the piston 2 has exactly two supports 4 – hereinafter referred to as 4a and 4b for clarity. The two supports 4a and 4b are formed simultaneously in method 1 in measure c). The core body 3 and the supports 4a and 4b are rotationally symmetrical with respect to the longitudinal center axis LMA. The core body 3 and the support 4a are hollow cylindrical, and the support 4b is cup-shaped. The core body 3 is arranged axially between the supports 4a and 4b. The support 4a and the core body 3 form sections of the wall 5, and the support 4b forms sections of the wall 5 and the entire bottom 6.

[0063] Fig. 10 shows a sectional view of the piston 2 according to the invention in a ninth embodiment. The piston 2 is manufactured using the method 1 described above. In the ninth embodiment of the piston 2, the core body 3 and the support 4 are rotationally symmetrical with respect to the longitudinal center axis LMA. Here, the core body 3 is hollow cylindrical and the support 4 is cup-shaped. The core body 3 is arranged externally around the support 4. The support 4 completely forms the inner region 5a of the wall 5 and the entire base 6. The core body 3 is axially shorter than the support 4 and forms the outer region 5b of the wall 5 only 29.10.2025

[0064] 13 sections. The core body 3 also lies here in the recess 9 of the support 4, so that the wall 5 facing away from the interior 7 is completely step-free or flat.

[0065] Fig. 11 shows a sectional view of the piston 2 according to the invention in a tenth embodiment. The piston 2 is manufactured using the method 1 described above. In the tenth embodiment of the piston 2, the core body 3 and the support 4 are rotationally symmetric with respect to the longitudinal center axis LM A. Here, the core body 3 is hollow cylindrical and the support 4 is cup-shaped. The core body 3 is arranged within the support 4 and is completely surrounded by the support 4. The support 4 here forms the entire inner region 5a of the wall 5, the outer region 5b of the wall 5, and the entire base 6. The core body 3 is axially shorter than the support 4 and lies within the support 4.

[0066] Fig. 12 shows a sectional view of the piston 2 according to the invention in an eleventh embodiment. The piston 2 is manufactured using the method 1 described above. In the eleventh embodiment of the piston 2, the core body 3 and the support 4 are rotationally symmetrical with respect to the longitudinal center axis LM A. Here, the core body 3 is hollow cylindrical and the support 4 is cup-shaped. The core body 3 is arranged within and surrounded by the support 4. The support 4 completely forms the inner region 5a of the wall 5, the outer region 5b of the wall 5, and the entire base 6. The core body 3 is axially shorter than the support 4 and lies within the support 4. The core body 3 extends to the edge 8 of the piston 2.

[0067] October 9, 2025

[0068] 14

[0069] Reference symbol list

[0070] 1 Procedure

[0071] Pistons

[0072] 3 core bodies, 4a, 4b support

[0073] 5 wall

[0074] 5a Interior of the wall

[0075] 5b Exterior of the wall

[0076] Floor

[0077] 6a Interior of the floor

[0078] 6b Exterior of the floor

[0079] 7 Interior

[0080] 8 rand

[0081] 9 In-depth study

[0082] LMA longitudinal center axis

Claims

October 29, 2025 15 Patent claims 1. Method (1) for manufacturing a piston (2) for a thermoacoustic heat pump, wherein the piston (2) has a core body (3) and at least one support (4), comprising the following measures in the following order: a) providing the core body (3) from a metallic material; b) Arranging the core body (3) in a molten first Al-Si alloy to produce an intermetallic Alfinier layer from the material of the core body (3) and the first Al-Si alloy on the surface of the core body (3), c) producing the at least one support (4) by at least partially overmolding the core body (3) with a molten second Al-Si alloy on the non-solidified intermetallic Alfinier layer on the core body (3), such that an intermetallic compound is formed between the intermetallic Alfinier layer on the core body (3) and the second Al-Si alloy and thereby the at least one support (4).

2. Method (1) according to claim 1, characterized in that, - that after measure c) in measure d) the core body (3) and the at least one support (4) are cooled so that the piston (2) is completed in which the core body (3) and the at least one support (4) are metallurgically bonded via the intermetallic Alfinier layer, and / or - that after measure c) in measure e) the piston (2) is finished, and / or - that after measure c) in measure f) the piston (2) is coated at least section by section with a sliding coating.

3. Method (1) according to claim 1 or 2, characterized in that, October 29, 2025 16 that in measure a) the core body (3) is provided made of iron or of steel or of a magnetic or magnetizable material.

4. Method (1) according to one of the preceding claims, characterized in that in measure a) the core body (3) is provided as a rotationally symmetric or n-fold rotationally symmetric body with respect to a longitudinal central axis (LMA) of the piston (2).

5. Method (1) according to one of the preceding claims, characterized in that the first Al-Si alloy used in measure b) and the second Al-Si alloy used in measure c) differ at least in the Si content.

6. Piston (2) for a thermoacoustic heat pump comprising a core body (3) and at least one support (4), wherein the piston (2) is manufactured in the method (1) according to one of claims 1 to 5.

7. Piston (2) according to claim 6, characterized in that - that the piston (2) has a wall (5) circumferentially spaced from its longitudinal central axis (LMA) and a bottom (6) oriented perpendicular to its longitudinal central axis (LMA), and - that the piston (2) has an interior space (7) which is partially limited to the outside by the wall (5) and the bottom (6).

8. Piston (2) according to claim 7, characterized in that, - that the core body (3) forms at least the wall (5) and / or at least the bottom (6) in sections, and / or October 29, 2025 17 - that at least one support (4) forms at least sectionally the wall (5) and / or at least sectionally the bottom (6).

9. Piston (2) according to claim 7 or 8, characterized in that, - that the core body (3) forms at least in sections an outer surface (5b) of the wall (5) facing away from the interior space (7) and / or at least in sections an inner surface (5a) of the wall (5) facing the interior space (7), and / or - that the core body (3) forms at least in sections an outer area (6b) of the base (6) facing away from the inner area (7) and / or at least in sections an inner area (6a) of the base (6) facing the inner area (7).

10. Piston (2) according to one of claims 7 to 9, characterized in that, - that at least one support (4) forms at least partially an exterior area (5b) of the wall (5) facing away from the interior space (7) and / or at least partially an interior area (5a) of the wall (5) facing the interior space (7), and / or - that the at least one support (4) forms at least in sections an outside area (6b) of the floor (6) facing away from the interior space (7) and / or at least in sections an inside area (6a) of the floor (6) facing the interior space (7).

11. Thermoacoustic heat pump with a housing, - wherein the heat pump comprises at least one piston (2) according to one of claims 6 to 10 and at least one drive unit for driving the at least one piston (2), and - wherein the at least one piston (2) and the at least one drive unit are arranged to interact electromagnetically with each other in the housing.

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