Metallic package for magnets in permanent magnet thrusters

Abstract

The invention relates to a permanent magnet thruster having a rotor yoke comprising a tubular element carrying a plurality of permanent magnets on or at a lateral surface of the tubular element. In a preferred embodiment, a plurality of permanent magnets are encapsulated in a magnet package made of a metal subjected to HIPping.

Description

TECHNICAL FIELD

[0001] The present invention relates to a permanent magnet thruster having a rotor yoke comprising a tubular element carrying a plurality of permanent magnets on or at a lateral surface of the tubular element. In a preferred embodiment, the plurality of permanent magnets is encapsulated in a magnet encapsulation made of a metal subjected to a HIPping process. BACKGROUND

[0002] Thrusters are widely used for propelling and / or maneuvering marine vessels. Such thrusters are designed to provide a thrust that rotates a plurality of propeller blades that are immersed in water below a vessel design waterline. Many such thrusters comprise a plurality of permanent magnets arranged on a rotor (rotor yoke). The propeller blades are connected at one end to the rotor and at the other end to a hub, allowing the rotor and propeller blades to rotate around the hub. Rotation is provided by a plurality of stator coils that can be magnetized by an electric current. This configuration of permanent magnets and magnetizable stator coils operates as an electric motor to provide rotation of the rotor.

[0003] Permanent magnets are made of a material that is susceptible to corrosion when exposed to a specific sea water (salted water). For example, neodymium type magnets are very susceptible to corrosion, even a small amount of moisture in the atmosphere can easily cause the magnets to corrode. Corrosion of permanent magnets is highly undesirable, as the magnets deteriorate in strength, shape, size, which results in a degradation of the magnetic strength of the magnets over time. In addition to this, the chemical substances generated due to corrosion can be a substance that should not be released into the sea water, and the formation of such chemical substances poses an additional environmental problem, as such chemical substances can be released from the magnets.

[0004] As corrosion occurs due to the close contact between the sea water and the surface of the permanent magnets, a covering of the surface of the permanent magnets can be chosen to avoid such close contact.

[0005] However, such a covering should have sufficient strength to withstand the harsh conditions in sea water, and should not reduce the magnetic strength of the permanent magnets to a large extent.

[0006] Furthermore, when considering a covering of the permanent magnets, the manufacturing process should be relatively simple to avoid introducing too much manufacturing cost in the production of the thruster.

[0007] Therefore, a thruster having an improved corrosion resistance would be advantageous, and in particular a more effective and / or reliable corrosion resistance of the permanent magnets used in the thruster would be advantageous.

[0008] OBJECT OF THE INVENTION

[0009] It is an object of the present invention to provide a thruster for marine use comprising permanent magnets, wherein corrosion of the permanent magnets is at least mitigated.

[0010] It is a further object of the present invention to at least mitigate corrosion of permanent magnets in a thruster for marine use in a way that allows for use in harsh conditions in seawater.

[0011] It is a further object of the present invention to at least mitigate corrosion of permanent magnets in a thruster for marine use in a way that preferably does not significantly reduce the magnetic field strength of the permanent magnets or even has the same higher magnetic strength.

[0012] It is a further object of the present invention to at least mitigate corrosion of permanent magnets in a thruster for marine use in a relatively simple manufacturing process.

[0013] It is a further object of the present invention to provide an alternative to the prior art. SUMMARY

[0014] Therefore, in a first aspect of the present invention, the above mentioned objects and a number of other objects are intended to be achieved by providing a permanent magnet thruster comprising:

[0015] a rotor yoke comprising:

[0016] a tubular element carrying a plurality of permanent magnets on or at a lateral surface of the tubular element;

[0017] a plurality of propeller blades extending inwardly from the tubular element to a hub rotatably arranged on a shaft;

[0018] a stator yoke arranged outside the rotor yoke and comprising a plurality of stator coils magnetizable by an electric current,

[0019] wherein

[0020] the plurality of permanent magnets and the plurality of stator coils are mutually configured such that the rotor yoke rotates when the plurality of stator coils is magnetized, and

[0021] the plurality of permanent magnets is encapsulated in a magnet encapsulation made of a metal subjected to HIPping, the magnet encapsulation encapsulating at least an open surface of the permanent magnets facing away from the lateral surface in a radial direction of the tubular element, an open surface facing in an axial direction of the tubular element and an open surface facing in a tangential direction of the tubular element.

[0022] The metal of the magnet encapsulation is preferably made of stainless steel, titanium, bronze, in particular nickel-aluminum-bronze and / or a corrosion-resistant alloy.

[0023] The package subjected to HIPping has some very characteristic material properties, such as an increase in density (due to shrinkage) compared to other processes such as sintering or casting, and a reduction in the content of impurities in the adsorbed gas.

[0024] Due to the presence of the package enclosing at least the open surface of the permanent magnet, and the use of sea water for HIPping substantially prevents contact with the open surface of the permanent magnet. HIPping provides shrinkage of the package, thereby providing an excellent seal at the interface between the open surface of the permanent magnet and the inner surface of the package.

[0025] Although it is preferred to completely enclose the permanent magnet, some surface area of the permanent magnet is placed in close contact with the surface of the tubular element, whereby it can be sufficient to enclose only some surface area, such as the open surface disclosed herein. Completely enclosing preferably means that no surface of the permanent magnet is exposed to the outside of the package.

[0026] The terms used herein are used in the way commonly used by the person skilled in the art. Some of the commonly used terms are explained in more detail below:

[0027] The Hot Isostatic Processing (HIPping) referred to herein as HIPping is a manufacturing process in which one or more permanent magnets are enclosed in a package preform made of metal, preferably stainless steel. The preform with the magnets is subjected to high temperature to remove adsorbed gas, if any, and subsequently compressed under elevated isostatic pressure while maintaining the high temperature by exposing the preform to an inert gas, such as argon, whereby the preform shrinks to form a magnet package. The magnet package is therefore said to be made by being subjected to HIPping, and the material resulting from HIPping is said to be HIPed material.

[0028] The open surface (of the permanent magnet) used herein preferably means a surface of the magnet that does not abut another surface before the magnet package is provided and / or a surface that does not face water during use of the magnet.

[0029] The thruster used herein refers to a marine thruster, which is a device for generating hydraulic thrust, preferably a directed thrust. The thruster is mounted on a vessel and used for maneuvering and / or propulsion. BRIEF DESCRIPTION OF DRAWINGS

[0030] The application will now be described in more detail, particularly with respect to preferred embodiments thereof, with reference to the accompanying drawings. The drawings show various ways of implementing the application and should not be construed as limiting to other possible embodiments falling within the scope of the appended claims.

[0031] Figure 1A three-dimensional view of a rotor yoke according to a preferred embodiment of the application is schematically shown; for the sake of clarity, only one propeller blade and three permanent magnets are shown,

[0032] Figure 2A A three-dimensional view of a rotor yoke according to a preferred embodiment of the application is schematically shown; for the sake of clarity, only one propeller blade and three permanent magnets are shown, Figure 2A ) and a corresponding stator yoke ( Figure 2B ),

[0033] Figure 3A A section according to a preferred embodiment of the application is schematically shown; Figure 3A The section is shown in a three-dimensional representation, and Figure 3B A cross-sectional view of the section in Figure 3A is shown, Figure 3C A section according to a preferred embodiment of the application is schematically shown; for the sake of clarity, only one propeller blade and three permanent magnets are shown,

[0034] Figure 4A The steps involved in making a magnet packaging section according to a preferred embodiment are schematically shown. Figure 4A The cross-sectional view shown is a cross-sectional view along the line A-A shown in Figure 3A .

[0035] Figure 5 An embodiment of a magnet packaging section is shown, in which the orientation of the magnets is different from the orientation disclosed in Figure 4B .

[0036] Figure 6 An embodiment of a magnet packaging section is shown, in which the orientation of the magnets is different from the orientation disclosed in Figure 4B . DETAILED DESCRIPTION

[0037] Reference is made to Figure 1 A rotor yoke 2 for a permanent magnet thruster in a first preferred embodiment is schematically shown.

[0038] The rotor yoke 2 is part of a thruster for providing maneuvering and / or propulsion of a vessel through a body of water by being submerged in water and connected to the vessel and rotating the propeller blades. The thruster can be an azimuth thruster, but the application is not limited to such an azimuth thruster.

[0039] In Figure 1In the disclosed embodiment, the rotor yoke 2 comprises a tubular element 3. The tubular element 3 is generally a tubular structure having an outwardly facing lateral surface and an inwardly facing lateral surface. A lateral surface is generally a surface facing a direction having a normal vector with a component in the radial direction of the thruster. The tubular element 3 of Fig. 3 carries a plurality of permanent magnets 4 on or at the outwardly facing lateral surface 5 of the tubular element 3. However, the permanent magnets 4 can be carried on the inwardly facing lateral surface. Carrying the magnets on or at the lateral surface generally refers to a situation in which the magnets are connected to the tubular element 3 in such a way that the rotational torque provided by the magnets (in an electric motor configuration) provides rotation of the tubular element 3. "At the lateral surface 5" refers to the permanent magnets 4 being placed at a distance from the lateral surface 5.

[0040] A plurality of propeller blades 10, such as five, six, seven, eight or more, are arranged to extend inwardly from the tubular element 3 to the hub 11. The hub 11 is arranged to be rotatable in the direction of the arrow 13. The hub 11 is arranged to be rotatable in the direction of the arrow 13. Figure 1 In the disclosed embodiment, only one such propeller blade 10 is shown (for clarity), although in practice more propeller blades are provided. Such propeller blades 10 are generally equally spaced in the circumferential direction, for example to avoid introducing vibrations during rotation. The propeller blades 10 are each rotatably arranged on a shaft 12. The shaft 12 forms part of a structure (not shown) connecting the thruster with a vessel.

[0041] On the outside of the rotor yoke 2, a stator yoke is arranged in a conventional manner for a permanent magnet thruster. The stator yoke comprises a plurality of stator coils which can be magnetized by an electric current. Thereby, the combination of the rotor yoke 2 and the stator yoke is similar to an electric motor, because when the stator coils are magnetized, the rotor yoke 2 will rotate (unless a force acting on the rotor is larger than can be overcome). The plurality of permanent magnets 4 and the plurality of stator coils are therefore configured with respect to each other such that the rotor yoke 2 rotates when the plurality of stator coils are magnetized.

[0042] Generally, permanent magnets are made of a material which is susceptible to corrosion, and such corrosion is obviously a disadvantage because it causes the magnets to degrade in terms of magnetic properties and in terms of size. Such corrosion is particularly pronounced in a marine environment involving sea water, in which the salt in the water causes the corrosion to develop rapidly.

[0043] To avoid corrosion of the permanent magnets, the permanent magnets are encapsulated in a magnet encapsulation 20 made of metal. Such encapsulation 20 is designed to shield the open surfaces of the magnets that would be exposed to water during use of the thruster if not encapsulated. As will be clear from the following, such shielding can be provided by fully encapsulating the permanent magnets or by only encapsulating the open surfaces that would otherwise be exposed to water. For the latter case, in one embodiment, the magnets are arranged on the lateral surface 5 such that one or more open surfaces are outwardly facing open surfaces and one or more surfaces are inwardly facing, e.g. abutting the lateral surface 5, whereby no water proof barrier is needed. In such embodiments, the encapsulation 20 covers the outwardly facing open surfaces.

[0044] It is generally preferred that the magnet encapsulation 20 encapsulates at least the open surfaces of the permanent magnets 4 that are facing away from the lateral open surfaces 5 in the radial direction, tangential direction and axial direction of the tubular element 3.

[0045] The encapsulation 20 can be a tubular element, within which the permanent magnets are fully or partially comprised (with the surfaces of the permanent magnets facing the lateral surface 5 of the tubular element 3), or the encapsulation 20 can be composed of multiple encapsulation segments 21, as Figure 2A illustrated.

[0046] Hence, the magnet encapsulation 20 encapsulates at least the open surfaces of each permanent magnet 4 that are facing away from the lateral open surfaces 5 and the open surfaces that are facing the axial direction of the tubular element 3. However, alternatively, the magnet encapsulation 20 can fully encapsulate all permanent magnets 4.

[0047] The magnet encapsulation 20 is made, inter alia, by HIPping an encapsulation preform in which one or more permanent magnets are enclosed. The preform is made of metal, preferably stainless steel. The preform can be a machined element, such as an element made by a material removal process or a sintering process, and the machined element comprises a compartment configured to receive the one or more permanent magnets, typically in a tight fit. In case the permanent magnets are arranged in the compartment, the preform with magnets is subjected to a high temperature to remove adsorbed gases, if any, after which the preform is compressed by exposing the preform to an inert gas, such as argon, under elevated isostatic pressure while maintaining the high temperature. This provides a shrinkage of the preform to form the magnet encapsulation.

[0048] In some embodiments, when the magnet encapsulation 20 is in the form of a tubular element, the magnet encapsulation 20 can be arranged on the tubular element 3 in a press fit manner, e.g. assisted by heating or cooling one of the elements by a heat shrink process. Alternatively or in combination, the magnet encapsulation 20 can be fastened by screws, welding or gluing.

[0049] As Figure 2A illustrated, the magnet package can comprise a plurality of magnet package segments 21. In Figure 2A particular, one such package segment is highlighted with a dashed line. Each magnet package segment 21 is made of metal and is subjected to HIPping. Such magnet package segments 21 can comprise a single permanent magnet or a group of permanent magnets.

[0050] In embodiments in which only one permanent magnet 4 is packaged, the permanent magnet is typically packaged by a magnet package segment 21 (see Figure 3A ) that packages at least the open surfaces of the permanent magnet 4 that face away from the lateral surface 5 in the radial direction of the tubular element 3, the open surfaces that face in the axial direction, and the open surfaces that face in the tangential direction. Figure 1 The “radial”, “tangential” and “axial” directions are illustrated in . With such packaging, the open surfaces of the magnet that would be exposed to water if not packaged are covered by the package, while the surfaces of the magnet that face the tubular element 3 can not be packaged. However, as will be described in detail below, it is typically preferred to fully package the magnet.

[0051] Figure 1 When the magnet package segment 21 comprises a group of permanent magnets, such magnets are typically arranged side-by-side in the tangential direction of the tubular element 3 (the orientation of such magnets is illustrated in

[0052] Also in such embodiments, the magnet package segment 21 packages at least the open surfaces of the group of magnets 4 that face away from the lateral surface 5 in the radial direction of the tubular element 3, the open surfaces that face in the tangential direction of the tubular element 3, and the open surfaces that face in the axial direction of the tubular element 3.

[0053] Note that while the permanent magnets can be cuboids, the present invention is not limited to such cuboid-shaped magnets. When non-cuboid magnets are used, they will still have open surfaces that face in the above-disclosed directions, although such open surfaces can be part of curved open surfaces.

[0054] In summary, the magnet package segment 21 can preferably be disclosed as a structure that protects the magnets from exposure to water when arranged on the tubular segment 3.

[0055] The orientation of the magnets 4, and thus the magnetization direction of the magnets relative to the stator yoke, can be determined in accordance with conventional practice in the technical field of permanent magnet thrusters to provide an electric motor design.

[0056] In some preferred embodiments, the magnet encapsulation section 20 encapsulates a group of four or more permanent magnets 4 arranged side-by-side in the tangential direction of the tubular element 3. The group of four or more permanent magnets may preferably be arranged into two or more subgroups, wherein the tangential distance between the permanent magnets 4 within a subgroup is less than the tangential distance between subgroups, for example, essentially zero.

[0057] In a preferred embodiment, the magnet encapsulation section 21 further encapsulates the opening surface of each permanent magnet 4 facing the lateral surface 5 on the axial direction of the tubular element 3, thereby completely encapsulating one or more permanent magnets 4 within the magnet encapsulation section 21.

[0058] Referring to Figure 3, a preferred embodiment of section 21 is shown. Figure 3A The magnet packaging section 21 is shown in a three-dimensional view, while Figure 3B It is along Figure 3A The figure shows a cross-sectional view of line AA. In the disclosed embodiment of FIG3, the magnet is completely encapsulated by the magnet encapsulation segment 21 to form an encapsulated magnet segment.

[0059] Figure 3B An optional backing element 22 is also disclosed. As shown, the magnet encapsulation section 21 further encapsulates the backing element 22, which is disposed between the lateral surface 5 of the tubular element 3 (as shown in FIG. 2 when the section is disposed on the tubular element 3) and the adjacent surface of the permanent magnet 4 facing the lateral surface 5 of the tubular element 3. In the illustrated embodiment, the magnet encapsulation section 21 further encapsulates the surface of the backing element 22 facing the lateral opening surface 5 and the axial and tangential surfaces of the backing element 22 facing the tubular element 3, thereby completely encapsulating the permanent magnet 4 and the backing element 22 within each section 21.

[0060] The backing element 22 is particularly useful in embodiments where the magnet encapsulation section 21, having a permanent magnet 4, is fastened to the rotor yoke 2 by screws. In such embodiments, an internal thread can be provided in the backing element, which can be accessed through an opening provided in the portion of the magnet encapsulation section 21 facing the lateral surface 5. Thus, the magnet encapsulation section 21 can be attached by screws extending through the tubular element 3, such as... Figure 2A Screw 18 is shown.

[0061] The backing element 22 is made of a material that can be used for HIPping the connection, which means that the compression of the backing element 22 is comparable to the compression of the permanent magnets when the magnet package section is subjected to HIPping, to avoid or at least minimize geometrical distortion of the magnet package section 22 due to HIPping. Preferably, the backing element 22 is made of the same metal as the package, although another metal can be used, preferably a metal different from the metal of the magnet package, such as carbon steel.

[0062] In preferred embodiments, at least some of the permanent magnets 4 are arranged side-by-side in a tangential direction of the tubular element 3, with a tangential distance between the permanent magnets 4 being greater than zero. In such embodiments, the permanent magnets 4 are preferably arranged equidistantly in the tangential direction.

[0063] In preferred configurations of permanent magnets, at least some of the permanent magnets 4, such as all of the permanent magnets 4, each have two side surfaces facing in a tangential direction of the tubular element 3, and wherein at least some of the permanent magnets 4, such as all of the permanent magnets 4, are arranged such that two permanent magnets 4 adjacent to each other abut each other along at least a portion of the side surfaces.

[0064] As many of the preferred embodiments of the thruster will be used in sea water, and although some corrosion in the magnet package or magnet package section can be acceptable, it is generally preferred to prevent or at least mitigate corrosion to the magnet package / magnet package section. To achieve this, the metal from which the magnet package / magnet package section is made is a corrosion resistant material, such as stainless steel.

[0065] As described herein, the permanent magnets 4 are preferably arranged side-by-side on an outer side of the tubular element 3 or on an inner side of the tubular element 3. However, due to efficiency improvements, it is preferred to arrange the permanent magnets on an outer side of the tubular element 3. The inner side refers to the side facing the hub 11; the outer is the opposite side.

[0066] As the tubular element 3 on or at which the magnet package 20 or magnet package section 21 will generally be arranged generally has a curvature (e.g. a radius of the tubular element 3), it is preferred to shape the outer surface 6 of the magnet package 20 or magnet package section 21 to have a curvature (R) coinciding with the tangential direction of the tubular element 3. However, in Figure 3A In the embodiment shown in -C, the part of the magnet package section facing the tubular element 3 (the bottom surface) is made flat. The surface of the tubular element 3 is shaped to be flat by including a recess as shown in -D. Figure 3CThe segmented flat surface is shown to simulate a flat surface (where only one magnet packaging element 21 is shown to make the surface of the tubular element 3 visible). It is also preferred that the surface of the packaging 20 or packaging segment 21 is provided with a curvature at a distance from the surface of the tubular element 3, as this will allow for a smaller gap between the rotor yoke 2 and the stator yoke.

[0067] The making of the magnet packaging 20 or magnet packaging segment 21 that packages the permanent magnets will now be described in detail with reference to the magnet packaging segment disclosed in Fig. 3 and shown in Fig. 4. For ease of reference to Fig. 3, the process in Fig. 4 is shown with the same orientation as the magnet packaging segment 21, although in actual implementations the magnet packaging segment 21 can advantageously be made with the orientation inverted (relative to the orientation of Fig. 4).

[0068] In Figure 4B the example of the orientation of the poles of the magnets 4 is also indicated with the symbol "N" for the North pole and with the symbol "S" for the South pole. Figure 4B The opposite polarity shown in can be achieved by magnetization. The magnet packaging segment 21 is pressed down using a device and the underlying individual magnets are magnetized. If the magnets are loose objects, they will move and attract each other. However, as the magnets are essentially stuck in place within the magnet packaging segment, they cannot move and will thus generate the necessary magnetic field to allow for subsequent rotation.

[0069] Figure 5 In Figure 5 is disclosed an example of another orientation of the poles within the magnet packaging segment 21, indicated with the symbol "N" for the North pole and with the symbol "S" for the South pole. Figure 4B the same cross-sectional view A-A as for

[0070] In Figure 6 is disclosed an example of another orientation of the poles within the magnet packaging segment 21, indicated with the symbol "N" for the North pole and with the symbol "S" for the South pole. Figure 5 the same cross-sectional view A-A as for Figure 4B

[0071] First, a preform 27 is made. The preform 27 can be provided by a sintering process or a material removal process such as milling or turning. The preform contains a cavity 29 shaped and dimensioned to receive the permanent magnets 4 and the backing element 22, preferably both in a tight fit. The preform 27 is shown in cross-sectional view in Figure 4A .

[0072] With the preform 27 made, and with reference to Figure 4B ​A permanent magnet 4 is placed in the cavity 29, and the permanent magnet is oriented and positioned at the intended location within the magnet encapsulation section 21. Then, as shown, a backing element 22 is placed in the cavity and adjacent to the surface of the permanent magnet 4. A closing member 28 is placed to close the opening of the cavity that has received the permanent magnet 4 and the backing element 22.

[0073] The sealing component 28 is then welded to the preform 27 to create a sealed vacuum unit, which is reinforced by hipping.

[0074] It should be noted that the closure component 28 and the preform are preferably made of the same material.

[0075] The method of providing the magnet encapsulation section 21 can be applied to a single permanent magnet or a group of permanent magnets, such as multiple permanent magnets. Figure 4B As shown, two permanent magnets 4 are arranged side by side in the preform 24. Although encapsulating different magnets in the encapsulation section 21 and using different magnets for the permanent magnet thruster is considered to be within the scope of the invention, it is generally preferred to encapsulate magnets of the same material in the encapsulation section 21 and to use magnets of the same material for the permanent magnet thruster.

[0076] The preform 27, having a magnet, backing element 22, and closure member 28, is subjected to hipping, such as Figure 4C As shown. HIPping is performed in pressure vessel 30, which is configured to withstand relatively high pressure and temperature during HIPping. During HIPping, both pressure (indicated by arrows marked "P") and temperature (indicated by arrows marked "Q") increase.

[0077] The HIPping process is typically performed at 900-1100 degrees Celsius and at a pressure of 100-200 MPa, using argon gas, with a residence time of 2-5 hours. After the HIP stage, the furnace is shut off and allowed to cool slowly to room temperature to avoid any residual stress or magnet breakage. While a suitable cooling rate for "slow cooling" can be found experimentally, in a preferred embodiment, the HIP furnace is shut off, and the encapsulated magnet is cooled from, for example, 1000°C to room temperature (e.g., 20°C) over 5 hours. Therefore, in a preferred embodiment, a cooling rate of 200°C per hour is used. However, a cooling rate of 100-300°C per hour has been found to be suitable for this invention.

[0078] Due to the tight fit mentioned above, shrinkage and shape changes after hipping are minimized, and this allows for easier final machining if needed. The hipping step also benefits the magnet itself by removing any internal porosity and improving its magnetic properties.

[0079] Permanent magnets used in connection with the preferred embodiments of the present application are preferably made of an alloy of neodymium, iron and boron to form Nd2Fe 14 NdFeB, SmCo5 and / or AlNiCo magnets. The permanent magnets in connection with the present application are preferably in solid form, i.e. not in powder form, before being encapsulated.

[0080] Before encapsulating one or more magnets in the magnet encapsulation section 21 and performing the HIPping process as described herein, the magnets can preferably be demagnetized, if not already non-magnetic or demagnetized. Such demagnetization has a number of advantages. Since neodymium magnets have a very high magnetic strength (when magnetized), it can be very difficult to place, for example, two magnets on top of each other Figure 4A Arranging the closing member 28 on the preform as shown can be a very challenging task. This is especially challenging in case the magnets are spatially separated as shown in Figure 4A and Figure 4B Especially in case the encapsulation material has magnetic properties. However, when demagnetized, the handling of the magnets becomes technically easier and with fewer safety issues.

[0081] After the HIPping process, the permanent magnets are magnetized. However, it is generally preferred to perform the magnetization after the encapsulated magnet section 21 has been arranged on the rotor yoke, since this makes it technically easier to apply the magnets to the rotor yoke than if the magnets are magnetized before being applied to the rotor yoke. When the magnetization is delayed until the encapsulated magnet section has been arranged on the rotor yoke, the magnet encapsulation section 21 can be machined, if needed, without having to take into account the difficulties that arise from the encapsulated magnet section being fastened to each other and / or to the machine used for machining the encapsulated magnet section by magnetic force.

[0082] The magnetization is performed by exposing the encapsulated magnets to a magnetic field.

[0083] It should be noted that depending on the permanent magnets used and the temperature during the HIPping process, the temperature of the magnets can exceed the Curie temperature of the magnets at which the magnets are demagnetized. Thus, in such embodiments, an active demagnetization does not introduce unwanted side effects.

[0084] In preferred embodiments, the HIPping process demagnetizes the magnets by the temperature during the HIPping process exceeding the Curie temperature of the permanent magnets to provide demagnetized permanent magnets.

[0085] Preferably, each permanent magnet is a magnetizable solid material, i.e. not a powder-like material, before said encapsulation and said HIPping.

[0086] Preferably, each permanent magnet is a neodymium magnet, a samarium-cobalt magnet and / or an AlNiCo magnet. Although it is considered to be within the scope of the present application to encapsulate different magnets within the encapsulation section 21, it is generally preferred to encapsulate magnets of the same material in the encapsulation section 21.

[0087] Although the present application has been described in connection with specific embodiments thereof, it will be understood that it is not intended to be limited to the examples presented, but is intended to cover alternatives, modifications, and equivalents. The scope of the present application is set out in the appended claims. In the context of the claims, the term "comprise" or "comprising" does not exclude the presence of other elements or steps than those listed in a claim. Furthermore, the reference signs in the claims shall not be construed as limiting the scope of the application. Moreover, individual features of the different claims can also be combined in other claims during the prosecution of the patent application without departing from the scope of the present application. Furthermore, the features of the embodiments described above can be combined in any combination without departing from the scope of the application.

[0088] List of items of the specific embodiments

[0089] Item 1. A permanent magnet thruster, comprising:

[0090] a rotor yoke (2) comprising:

[0091] a tubular element (3) carrying a plurality of permanent magnets (4) on or at a lateral surface (5) of said tubular element (3);

[0092] a plurality of propeller blades (10) extending inwardly from said tubular element (3) to a hub (11) rotatably arranged on a shaft (12);

[0093] a stator yoke arranged outside the rotor yoke (2) and comprising a plurality of stator coils magnetizable by electric current,

[0094] wherein,

[0095] said plurality of permanent magnets (4) and said plurality of stator coils are mutually configured such that said rotor yoke (2) rotates when said plurality of stator coils is magnetized, and

[0096] The plurality of permanent magnets is encapsulated in a magnet encapsulation (20) made of metal subjected to HIPping, which encapsulates at least an open surface of the permanent magnets (4) facing away from the lateral surface (5) in a radial direction of the tubular element (3), an open surface facing an axial direction of the tubular element, and an open surface facing a tangential direction of the tubular element.

[0097] Clause 2. The permanent magnet thruster (1) according to clause 1, wherein the magnet encapsulation (20) comprises a plurality of magnet encapsulation segments (21) made of metal and each subjected to HIPping, wherein each of the segments (21) encapsulates a single permanent magnet or a group of permanent magnets arranged side by side in a tangential direction of the tubular element (3), each of the single permanent magnet or the group of permanent magnets being encapsulated by a magnet encapsulation segment (21) encapsulating at least an open surface of each of the permanent magnet or the group of magnets (4) facing away from the lateral surface (5) in a radial direction of the tubular element (3), an open surface facing a tangential direction of the tubular element (3), and an open surface facing an axial direction of the tubular element (3).

[0098] Clause 3. The permanent magnet thruster (1) according to clause 2, wherein each of the magnet encapsulation segments (21) encapsulates a group of two, four or more permanent magnets (4) arranged side by side in a tangential direction of the tubular element (3), and wherein the group of four or more permanent magnets is arranged in two or more subgroups, wherein a tangential distance between permanent magnets (4) within the subgroups is smaller than a tangential distance between subgroups, for example substantially zero.

[0099] Clause 4. The permanent magnet thruster according to clause 2 or 3, wherein each of the magnet encapsulation segments (21) further encapsulates an open surface of each of the permanent magnets (4) facing towards the lateral open surface (5) in an axial direction of the tubular element (3), whereby the permanent magnets (4) within the magnet encapsulation segment (21) are completely encapsulated by the magnet encapsulation segment (21).

[0100] Clause 5. The permanent magnet thruster according to clause 2 or 3, wherein the magnet packaging section (21) further packages a backing element (22) arranged between the lateral surface (5) of the tubular element (3) and the abutting surface of the permanent magnet (4) facing towards the lateral surface (5) of the tubular element (3), and wherein each of the magnet packaging sections (21) further packages a surface of the backing element (22) facing towards the lateral opening surface (5) and a surface of the backing element (22) facing in axial and tangential direction of the tubular element (3), whereby the permanent magnet (4) and the backing element (22) within each of the sections (21) are completely packaged by the magnet packaging section (21).

[0101] Clause 6. The permanent magnet thruster according to clause 5, wherein the backing element (22) is made of metal, preferably of a different metal than the metal of the magnet packaging, such as carbon steel.

[0102] Clause 7. The permanent magnet thruster (1) according to any of the preceding clauses, wherein the permanent magnets are completely packaged by the magnet packaging.

[0103] Clause 8. The permanent magnet thruster according to any of the preceding clauses, wherein the metal of which the magnet packaging is made is selected from the group consisting of stainless steel, titanium and bronze, in particular nickel-aluminium-bronze.

[0104] Clause 9. The permanent magnet thruster according to any of the preceding clauses, wherein the permanent magnets (4) are arranged side by side on an outer side of the tubular element (3) or on an inner side of the tubular element (3).

[0105] Clause 10. The permanent magnet thruster according to clause 9, wherein the outer surface (6) of the magnet packaging (20) has a curvature (R) in tangential direction of the tubular element (3), or, when dependent on any of claims 2-6, the magnet packaging section (21) has a curvature (R) in tangential direction of the tubular element (3).

[0106] Clause 11. The permanent magnet thruster (1) according to any of the preceding clauses, wherein at least some of the permanent magnets (4) are arranged side by side in tangential direction of the tubular element (3), wherein the tangential distance between permanent magnets (4) is greater than zero, the permanent magnets (4) preferably being arranged equidistant in the tangential direction.

[0107] Clause 12. The permanent magnet thruster according to any of the preceding clauses, wherein at least some of the permanent magnets (4), such as all of the permanent magnets (4), each have two side-open surfaces facing in tangential direction of the tubular element (3), and wherein at least some of the permanent magnets (4), such as all of the permanent magnets (4), are arranged such that two of the permanent magnets (4) adjacent to each other abut each other along at least a portion of the side-open surfaces.

[0108] Clause 13. The permanent magnet thruster according to any of the preceding clauses, wherein the permanent magnets (4) are cuboids.

[0109] Clause 14. The permanent magnet thruster according to any of the preceding clauses, wherein the permanent magnets, prior to the encapsulation, each are a magnetizable solid material.

[0110] Clause 15. The permanent magnet thruster according to any of the preceding clauses, wherein the permanent magnets each are neodymium magnets, samarium-cobalt magnets and / or AlNiCo magnets.

[0111] Clause 16. A method of providing a section comprising a plurality of permanent magnets, wherein the one or more permanent magnets are arranged side-by-side and encapsulated by a magnet encapsulation section (21) such that the magnet encapsulation section completely encapsulates each of the one or more permanent magnets (4), the method comprising:

[0112] subjecting the one or more encapsulated magnets to a temperature in the range of 900-1100 degrees Celsius and a pressure in the range of 100-200 MPa in an argon atmosphere for a residence time of 2-5 hours, and

[0113] subsequently allowing the one or more encapsulated magnets to cool, such as to a temperature of approximately 200 degrees Celsius, preferably at a cooling rate in the range of 100-300 degrees Celsius per hour, to avoid any residual stress or cracking of the magnets.

[0114] Clause 17. The method according to clause 16, wherein the HIPping demagnetizes the one or more magnets, typically by subjecting the temperature to exceed the Curie temperature of the one or more permanent magnets, to provide one or more demagnetized permanent magnets.

[0115] Clause 18. The method according to clause 16, wherein the encapsulation section (21) comprises a preform (27) configured to receive the side-by-side magnets and a closing member (28) configured to close the preform (70), the method comprising the subsequent step of:

[0116] demagnetizing the permanent magnets to provide demagnetized permanent magnets;

[0117] arranging the demagnetized magnets in the preform (27) and closing the encapsulation section (21) by connecting, preferably by welding, the closing member (28) to the preform (27).

[0118] Clause 19. The method according to clause 16 or 17, wherein the demagnetized magnets are magnetized after the HIPping.

[0119] Clause 20. The method according to clause 19, wherein the magnetizing is performed after arranging the encapsulated magnet section on a rotor yoke of a permanent magnet thruster according to any of the preceding clauses 1-15.

[0120] Clause 21. The method according to any of the preceding clauses 16-20, wherein, prior to the encapsulating and the HIPping, the permanent magnets are each a magnetizable solid material.

[0121] Clause 22. The method according to any of the preceding clauses 16-21, wherein the permanent magnets are each a neodymium magnet, a samarium-cobalt magnet and / or an AlNiCo magnet.

[0122] List of used reference signs:

[0123] 1 thruster

[0124] 2 rotor yoke

[0125] 3 tubular element

[0126] 4 permanent magnet

[0127] 5 lateral surface

[0128] 6 outer surface

[0129] 10 propeller blade

[0130] 11 hub

[0131] 12 shaft

[0132] 18 screw

[0133] 20 magnet encapsulation

[0134] 21 magnet encapsulation section

[0135] 22 backing element

[0136] 24 axial direction

[0137] 25 radial direction

[0138] 26 tangential direction

[0139] 27preform

[0140] 28closure member

[0141] 29cavity

[0142] 30pressure tank

[0143] Rcurvature

Claims

1. A permanent magnet thruster, comprising: a rotor yoke (2) comprising: a tubular element (3) carrying a plurality of permanent magnets (4) on or at a lateral surface (5) of the tubular element (3); a plurality of propeller blades (10) extending inwardly from the tubular element (3) to a hub (11) rotatably arranged on a shaft (12); a stator yoke arranged outside the rotor yoke (2) and comprising a plurality of stator coils magnetizable by electric current, wherein the plurality of permanent magnets (4) and the plurality of stator coils are mutually configured such that, when the plurality of stator coils is magnetized, the rotor yoke (2) rotates, and the plurality of permanent magnets is encapsulated in a magnet encapsulation (20) made of metal subjected to hot isostatic pressing (HIPping), the magnet encapsulation (20) encapsulating at least an open surface of the permanent magnets (4) facing away from the lateral surface (5) in a radial direction of the tubular element (3), an open surface facing an axial direction of the tubular element (3), and an open surface facing a tangential direction of the tubular element (3).

2. The permanent magnet thrust engine (1) according to claim 1, wherein, the magnet encapsulation (20) comprises a plurality of magnet encapsulation segments (21) made of metal, and each magnet encapsulation segment is subjected to HIPping, wherein each of the magnet encapsulation segments (21) encapsulates a single permanent magnet or a group of permanent magnets arranged side by side in a tangential direction of the tubular element (3), each of the single permanent magnet or the group of permanent magnets being encapsulated by the magnet encapsulation segment (21) encapsulating at least an open surface of each of the permanent magnets or the group of magnets (4) facing away from the lateral surface (5) in a radial direction of the tubular element (3), an open surface facing a tangential direction of the tubular element (3), and an open surface facing an axial direction of the tubular element (3).

3. The permanent magnet thrust engine (1) according to claim 2, wherein, each of the magnet encapsulation segments (21) encapsulates a group of two, four or more permanent magnets (4) arranged side by side in a tangential direction of the tubular element (3), and wherein the group of four or more permanent magnets is arranged in two or more subgroups, wherein a tangential distance between permanent magnets (4) within the subgroups is smaller than a tangential distance between subgroups, for example substantially zero.

4. The permanent magnet thrust engine of claim 2 or 3, wherein, each of the magnet encapsulation segments (21) also encapsulates an open surface of each of the permanent magnets (4) facing towards the lateral open surface (5) in an axial direction of the tubular element (3), whereby the permanent magnets (4) within the magnet encapsulation segment (21) are completely encapsulated by the magnet encapsulation segment (21).

5. The permanent magnet thrust engine of claim 2 or 3, wherein, The magnet packaging section (21) also packages a backing element (22) arranged between the lateral surface (5) of the tubular element (3) and the abutting surface of the permanent magnet (4) facing towards the lateral surface (5) of the tubular element (3), and wherein each of the magnet packaging sections (21) also packages a surface of the backing element (22) facing towards the lateral opening surface (5) and a surface of the backing element (22) facing towards the axial direction and the tangential direction of the tubular element (3), whereby the permanent magnet (4) and the backing element (22) within each of the sections (21) are completely packaged by the magnet packaging section (21).

6. The permanent magnet thrust engine of claim 5, wherein, The backing element (22) is made of metal, preferably of a different metal than the metal of the magnet packaging, such as carbon steel.

7. The permanent magnet thrust engine (1) according to any of the preceding claims, wherein, The permanent magnets are completely packaged by the magnet packaging.

8. The permanent magnet thrust engine of any of the preceding claims, wherein, The metal of which the magnet packaging is made is selected from the group consisting of stainless steel, titanium and bronze, in particular nickel-aluminium-bronze.

9. The permanent magnet thrust engine of any of the preceding claims, wherein, The permanent magnets (4) are arranged side by side on the outside of the tubular element (3) or on the inside of the tubular element (3).

10. The permanent magnet thrust engine of claim 9, wherein, The outer surface (6) of the magnet packaging (20) has a curvature (R) in the tangential direction of the tubular element (3), or, when dependent on any one of claims 2-6, the magnet packaging section (21) has a curvature (R) in the tangential direction of the tubular element (3).

11. The permanent magnet thrust engine (1) according to any of the preceding claims, wherein, The permanent magnets (4) are arranged side by side in the tangential direction of the tubular element (3), wherein the tangential distance between permanent magnets (4) is greater than zero, preferably the permanent magnets (4) are equally distanced in the tangential direction.

12. The permanent magnet thrust engine of any of the preceding claims, wherein, At least some of the permanent magnets (4), such as all of the permanent magnets (4), each have two side opening surfaces facing towards the tangential direction of the tubular element (3), and wherein at least some of the permanent magnets (4), such as all of the permanent magnets (4), are arranged such that two of the permanent magnets (4) adjacent to each other abut each other along at least a portion of the side opening surfaces.

13. The permanent magnet thrust engine of any of the preceding claims, wherein, The permanent magnets (4) are cuboids.

14. The permanent magnet thrust engine of any of the preceding claims, wherein, The permanent magnets are each magnetisable solid materials prior to the packaging.

15. The permanent magnet thrust engine of any one of the preceding claims, wherein, The permanent magnets are each neodymium magnets, samarium-cobalt magnets and / or AlNiCo magnets.

16. A method of providing a magnet packaging section comprising a single permanent magnet or a group of permanent magnets, such as a plurality of permanent magnets, the magnets of the group of permanent magnets being arranged side by side, the magnet or group of magnets being packaged by a magnet packaging section (21), whereby the magnet packaging section each completely packages one or more of the permanent magnets (4), the method comprising: by subjecting the one or more encapsulated magnet segments to a temperature in the range of 900-1100 degrees Celsius and a pressure in the range of 100-200 MPa in an argon atmosphere for a residence time of 2-5 hours, and subsequently allowing the one or more encapsulated magnet segments to cool, such as to a temperature of approximately 20 degrees Celsius, preferably at a cooling rate in the range of 100-300 degrees Celsius per hour, to avoid any residual stress or cracking of the magnets.

17. The method of claim 16, wherein, The HIPping typically demagnetizes the one or more magnets by subjecting the temperature to exceed the Curie temperature of the one or more permanent magnets, to provide one or more demagnetized permanent magnets.

18. The method of claim 16, wherein, The encapsulation segment (21) comprises a preform (27) configured to receive the side-by-side magnets and a closing member (28) configured to close the preform (70), the method comprising the subsequent steps prior to the HIPping: demagnetizing the one or more permanent magnets to provide one or more demagnetized permanent magnets; arranging the one or more demagnetized magnets in the preform (27) and closing the encapsulation segment (21) by connecting the closing member (28) to the preform (27), preferably by welding.

19. The method of claim 16 or 17, wherein, The demagnetized magnets are magnetized after the HIPping.

20. The method of claim 19, wherein, The magnetization is performed after arranging the encapsulated magnet segments on a rotor yoke of a permanent magnet thruster according to any of the preceding claims 1-15.

21. The method according to any of the preceding claims 16-20, wherein, Prior to the encapsulation and the HIPping, the permanent magnets are each magnetizable solid material.

22. The method according to any of the preceding claims 16-21, wherein, The permanent magnets are each neodymium magnets, samarium-cobalt magnets and / or AlNiCo magnets. The permanent magnets are each neodymium magnets, samarium-cobalt magnets and / or AlNiCo magnets.

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