apparatus

Abstract

The present invention is concerned with electrical propulsion systems and the removal of undesirable heat build up during the operation of such propulsion systems. Electrical propulsion systems have many benefits over combustion propulsion systems, particularly in relation to chemical emissions and the like. It is widely seen that electrical propulsion systems may render transport as more viable in a long term perspective. There are however a number of problems inherent in the use of electrical propulsion over traditional combustion propulsion systems. Combustion propulsion systems are extremely well suited to large scale propulsion due to their inherent energy density properties. In an attempt to increase the viability of electrical propulsion, attempts have been made to overcome such problems. We provide herein a further advancement in this area.

Description

[0001] Apparatus

[0002] Technical Field The present invention is concerned with electrical propulsion systems and the removal of undesirable heat build up during the operation of such propulsion systems.

[0003] Electrical propulsion systems have many benefits over combustion propulsion systems, particularly in relation to chemical emissions and the like. It is widely seen that electrical propulsion systems may render transport as more viable in a long term perspective.

[0004] There are however a number of problems inherent in the use of electrical propulsion over traditional combustion propulsion systems. Combustion propulsion systems are extremely well suited to large scale propulsion due to their inherent energy density properties. In an attempt to increase the viability of electrical propulsion, attempts have been made to overcome such problems. We provide herein a further advancement in this area.

[0005] Summary of the Invention

[0006] Aspects of the invention are set out in the accompanying claims.

[0007] Viewed from first aspect there is provided an electrically drivable motor for use in an aircraft, the motor comprising: a motor coil comprising a plurality of coil windings; a plurality of elongate thermally conductive members each arranged to thermally communicate with at least a portion of one of the plurality of coil windings; at least one thermally conductive portion arranged to thermally communicate with a plurality of elongate thermally conductive members, wherein a portion of at least one of the plurality of elongate thermally conductive members abuts a portion of at least one of the plurality of coil windings; and wherein each of the plurality of elongate thermally conductive members has an in use thermal conductivity of at least 100 Wnr’K’1and an electrical conductivity of less than 10'14Snr1.

[0008] Thus, according to an invention, thermal energy generated in an electrically drivable motor can be efficiently and effectively removed from the system without generation of currents that may give rise to additional undesirable thermal energy and a reduction in efficiency. Removal of thermal energy from the coil windings has a series of advantages in particular allowing the motor to be run at particularly high power levels. By using materials with specific properties for thermal conductivity and electrical resistivity, highly effective thermal energy removal can be provided while significantly reducing the likelihood of undesirable eddy currents or the like. The present arrangement has been shown to be highly effective at thermal transfer from the motor coil to the thermal energy carrier of the thermally conductive members. In use may refer to when the machine is operating, which may have a relevance to the temperature of the thermally conductive members. This temperature may be different to typical room temperature.

[0009] In effect, a plurality of heat transmission paths are provided by the plurality of elongate thermally conductive members, each being electrically isolated from other transmission paths to decreasing current build up and decreasing eddy currents. Decreasing eddy currents then decreases additional heat generation in such a system and is particularly desirable as the knock-on effects are significant. A greater amount of thermal energy can be effectively transferred while simultaneously a smaller thermally conductive portion can be provided for handling the thermal energy generation from the electrically drivable motor. This provides therefore a very compact, lightweight and therefore highly flight-efficient system. When arranged in an aircraft, for example, this increases the viability of electrical propulsion and therefore increases the likelihood of use over combustion engines. This in turn has a beneficial environmental impact.

[0010] In examples, a portion of at least one of the plurality of elongate thermally conductive members is connected to a portion of at least one of the plurality of coil windings.

[0011] The efficiency of the plurality of elongate thermally conductive members may be improved via connection to the plurality of coil windings. In example, some of the plurality of elongate thermally conductive members may be connected to some of the plurality of coil windings. In examples, each coil winding connects to at least one elongate thermally conductive member. This leads to highly effective removal of thermal energy from the coil. This also leads to a highly compact arrangement for the motor. Abutting between the elongate thermally conductive members and the coil windings allows excellent thermal transfer.

[0012] In examples, a portion of at least one of the plurality of elongate thermally conductive members is connected to a portion of at least one of the plurality of coil windings via at least one of laser ablation and a sol-gel process.

[0013] These processes have been shown to be highly effective for connecting unlike materials together. In particular, the motor coil is an electrical conductor while the thermally conductive members are effectively electrical insulators as such connection between two unlike materials may be difficult. The present inventors have found that this connection approach allows for a reliable connection between the elements. This improves the performance of the present system and improves the arrangement’s reliability of robustness.

[0014] High thermal conductivity and low electrical conductivity is highly desirable for the at least one thermally conductive portion as outlined above. The plurality of elongate thermally conductive members may be individually electrically isolated from one another. As such, the plurality of elongate thermally conductive members do not require low electrical conductivity. It may be advantageous for the thermally conductive members to have low electrical conductivity.

[0015] In examples, the plurality of elongate thermally conductive members are in the form of plates.

[0016] In the present discussion, plates may be deemed to be elements that are broadly 2D. In that, a plate is seen to be a structure with a length and width that are rather greater than the depth of the structure. The plates are highly effective at transferring away thermal energy from the motor coil windings.

[0017] In examples, the plurality of elongate thermally conductive members are interleaved with the plurality of coil windings.

[0018] In this arrangement, the thermally conductive members are interleaved with the coil windings. This may be in the form of an A-B-A-B structure, where each coil winding is connected to on either side by a thermally conductive member. This however may be in an A-A-B-B-A-A-B-B structure of the like. There is a broad alternating arrangement which provides for highly effective thermal transfer. In particular, this arrangement may reduce the likelihood and propensity of hot spots within the motor coil.

[0019] This improves overall thermal energy removal from the motor. In specific examples, the coil of the motor is maintained at or around 40 K or below. The plurality of elongate thermally conductive members may be maintained around about 25 to 40 K. The at least one thermally conductive portion may also be maintained around about 25 to 40 K. The temperature gradient between the coil and a cooling fluid used in the system to provide cooling may be around 5 K. In examples, the coolant may be arranged at around 20 K or above and the coils expect around 40 K or below. In examples, the coolant operationally is maintained around 30 K and the coils at around 35 K. This leads to a temperatures difference of less than around 25 K. The system proposed is highly thermally conductive as such the plurality of elongate thermally conductive members are likely to be at a similar temperature other than in the event that very large amounts of thermal energy are being transferred.

[0020] The cooling may be provided so that the coils of the motor may be maintained in a superconducting region. The cooling may be provided so that the coils of the motor may be maintained in a hyperconducting region. The coils may be of a high purity of material. The coils may be made of copper or aluminium or the like.

[0021] In examples, the plurality of elongate thermally conductive members are in the form of cables.

[0022] Cable form have been found to be more robust than other similar arrangements. Cable form may be formed single crystal material satisfying the above thermal conductivity. This is achievable and highly suitable for the arrangements discussed herein. Complex arrangements may be formed more easily with thermally conductive members in the form of cables. Other arrangements may be more brittle than cable form.

[0023] In examples, the plurality of elongate thermally conductive members are intermixed with the plurality of coil windings.

[0024] Intermixed in the present disclosure refers to the presence of thermally conductive members at locations along the length of the coil windings. The present arrangement provides removal of hot spots along the length of the coil windings without merely locating the thermally conductive members at one location or one main location with respect to the coil windings. The thermally conductive members may be interlaced with the coil windings so that there is contact along the full length of the coil windings.

[0025] In examples, the plurality of elongate thermally conductive members are evenly intermixed with the plurality of coil windings throughout a full length of the plurality of coil windings.

[0026] Even intermixing allows for a thoroughly even and therefore robust removal of thermal energy from the coil windings. An even intermixing vastly reduces the likelihood of hot spots. This reduces the likelihood of damage to the motor coil and therefore improves the lifetime of the motor.

[0027] In examples, the plurality of elongate thermally conductive members are wound into the plurality of coil windings.

[0028] In this arrangement, the construction of the motor may be more complex, however the thermally conductive members are alongside the coil windings along the entirety of the windings. Such an arrangement further reduces the likelihood of hot spots. This therefore further reduces the likelihood of damage to the motor coil and therefore improves the lifetime of the motor.

[0029] In examples, the plurality of coil windings has a length in a first axis of at least 20 cm. In examples, the motor coil has a length in a second axis of no more than 20 cm.

[0030] The present arrangement is functional with large a size of motor coil. The present arrangement is therefore suitable for high energy output motors for use in electrical aircraft of reasonable size. As such, the present arrangement is a significant shift in the direction of current use for such thermal energy management systems (TMSs). In particular, while small electrical aircraft exist, at present there are no large scale electrical aircraft. This arrangement improves the viability of large scale electrical aircraft. The present arrangements improves the feasibility of use of longer coil windings or running existing coil windings (i.e. at a standard size) at a higher power. This leads to the motor being either more powerful for the same size or more compact for the same power. Both are highly advantageous in aerospace applications.

[0031] In examples, the plurality of elongate thermally conductive members are formed from at least one of: single crystal sapphire; polycrystalline sapphire; amorphous sapphire; diamond; aluminium nitride; alumina; and, beryllium oxide. In examples, at least one thermally conductive portion is formed from at least one of: single crystal sapphire; polycrystalline sapphire; amorphous sapphire; diamond; aluminium nitride; aluminium; copper; and, beryllium oxide.

[0032] These materials have been found to be highly advantageous for the present arrangements. In particular, the present inventors have found that these materials have high thermal conductivity. The materials for the thermally conductive members have low electrical conductivity. In this way eddy currents can be strongly mitigated in the thermally conductive members. Furthermore, the arrangements (in the form of plates, cables, via intermixing, via winding) described above can be formed from these materials with considered construction. Each of these provide increasing advantages in regards to space and material use efficiency.

[0033] In examples, the plurality of elongate thermally conductive members are connected to the at least one thermally conductive portion via at least one of brazing, soldering, and metallising and soldering. This allows for a robust connection between the thermally conductive members (removing thermal energy from the motor coil windings) and the thermally conductive portion (to which the thermal energy is conducted). The thermally conductive portion may further carry the thermal energy onwards and away from the motor coil.

[0034] The arrangements above are highly effect and highly robust. The system is well designed for motors that are much more powerful or much larger than motors currently used in aircraft. For this reason, the present arrangements render more viable large sized aircraft operating entirely or partially on electrical propulsion.

[0035] Viewed from another aspect there is provided a propulsion system for an aircraft comprising: a cryogen source containing a cryogen for use in electrical energy generation; at least one fuel cell for generating electrical energy at least in part from the cryogen; the electrically drivable motor of any of the above aspects or examples; the at least one fuel cell arranged to provide electrical energy to the electrically drivable motor.

[0036] In examples, the at least one thermally conductive portion and the plurality of elongate thermally conductive members are in thermal communication with the cryogen, the cryogen arranged to provide a heat exchanger function to at least one of: the at least one thermally conductive portion; and, the plurality of elongate thermally conductive members.

[0037] Electrically powered aircraft use cryogen for production of electrical energy. This system further utilises the low temperature material for removal of thermal energy from the system (originating in the motor coils). This provides a number of advantages from the use of one cryogenic source (electrical production alongside thermal management).

[0038] In examples, the at least one thermally conductive portion comprises a conduit for carrying a fluid, wherein the conduit is in fluid communication with the cryogen in the cryogen source, and wherein in use a fluid cryogen from the cryogen source is arranged to be provided to the conduit and is arranged to flow through the conduit.

[0039] The thermally conductive portion may be cooled by a conduit through the conductive portion that carries a cryogen from the cryogen source. This improves the thermal transfer from the elongate thermally conductive members to the thermally conductive portion.

[0040] Viewed from another aspect there is provided an aircraft comprising the electrically drivable motor of any of the above aspects or examples or the propulsion system of any of the above aspects or examples.

[0041] Viewed from yet another aspect there is provided a method of operating the electrically drivable motor of any of the above aspects or examples, the propulsion system of any of the above aspects or examples or the aircraft of any of the above aspects or examples.

[0042] Viewed from yet another aspect there is provided a stator cooling arrangement comprising the electrically drivable motor of any of the above aspects or examples. In examples, the stator cooling arrangement further comprises a gas cooling arrangement for providing gas cooling to a stator. Gas cooling is a suitable option for effective removal of thermal energy.

[0043] The cryogen source discussed above may be a source of liquid helium or liquid hydrogen. Such a cryogen is highly effective for thermal energy removal and boiled hydrogen may be used in fuel cells, or in combustion, or the like for providing energy for the motor. The cryogen may be hydrogen, helium, nitrogen or the like, in liquid, gas, supercritical or solid phase. In an example, the cryogen may be frozen nitrogen or cryogenically frozen water.

[0044] The plurality of thermally conductive members may be in the form of a plurality of plates or cables or the like. Such arrangements are relatively simple to produce and integrate into the system well from a manufacturing view when a considered manufacturing approach is taken.

[0045] The cryogen source may be a cryogen distributor comprising a corresponding number of outlets in fluid communication with the plurality of conduits. This arrangement allows for effective cryogen distribution through the arrangement and is easy to construct from a mechanical position.

[0046] The cryogen source may be a user-controllable cryogen source arranged to controllably provide cryogen to the conduit or conduits.

[0047] This allows control for the user of active cooling from the cryogen for use in moments of high demand, such as take off or the like. Active cooling is an additional manufacturing difficulty to introduce, however it has been shown herein to be beneficial for thermal energy removal and in electrically driven aircraft propulsion, as cryogen may already be present. In essence, this arrangement takes advantage of aspects that may already be present in aircraft and therefore provides improved thermal energy removal performance without significantly increasing the additional manufacturing or structural difficulties.

[0048] The plurality of thermally conductive members may be arranged into a cable, in particular a spiral or helical winding. The thermally conductive members may be interleaved. The members may be intermixed with the motor coil windings for excellent transmission of thermal energy from the coil to the members. Such arrangements may be particularly space efficient, easy to manufacture and robust. Such arrangements may not be overly straightforward but provide advantageous thermal energy removal and vast reduction in the likelihood of hot spots in the coil windings.

[0049] In an example, the cryogen source and the conduit or conduits in the thermally conductive portion are arranged in a closed loop. In this way, the cryogen is returned to the source after use and cryogen is not required to be provided as regularly as would be the case where the system is not closed-loop.

[0050] Brief Description of the Drawings

[0051] One or more embodiments of the invention will now be described, byway of example only, and with reference to the following figures in which:

[0052] Figure 1 shows a schematic view of a portion of an electrically driveable motor for use in an aircraft according to examples;

[0053] Figure 2 shows a schematic view of a portion of an electrically driveable motor for use in an aircraft according to examples;

[0054] Figure 3 shows a schematic view of a portion of an electrically driveable motor for use in an aircraft according to examples;

[0055] Figure 4 shows a schematic view of a portion of an electrically driveable motor for use in an aircraft according to examples; and,

[0056] Figure 5 shows a schematic view of a portion of an electrically driveable motor for use in an aircraft according to examples.

[0057] Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

[0058] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc, other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

[0059] Detailed Description

[0060] An invention described herein relates to thermal energy conduction for use with an electrically drivable motor. A particular system for this invention may be an aircraft with a low temperature electrically drivable motor, or an electrically drivable motor utilising energy generated in low temperature environments.

[0061] Figure 1 shows a simple schematic of a portion 100 of an electrically driveable motor for use in an aircraft. The motor comprises a motor coil 110 comprising a plurality of coil windings. The motor comprises a plurality 120 of elongate thermally conductive members each arranged to thermally communicate with at least a portion of one of the plurality of coil windings.

[0062] In the example of Figure 1 , there are three coil layers shown as layers 112, 114, 116. There are elongate thermally conductive members extending through the arrangement. The elongate thermally conductive members 120 are in the form of plates. The plates have considerable length and widths but a much smaller depth. There are four thermally conductive members 122, 124, 126, 128 in the example of Figure 1. The thermally conductive members 120 are interleaved with the coil layers 112, 114, 116. Specifically, looking at coil layer 112, the layer 112 has thermally conductive member 122 below it and thermally conductive member 124 above it. The coil layer 112 may be described as abutting on either side a thermally conductive member. Specifically, the arrangement of Figure 1 is an A-B-A-B-A arrangement wherein the thermally conductive members are arranged either side of a coil layer.

[0063] The coil layer 112 may be a coil winding or a collection of coil windings. In a full scale arrangement, the inventors envisage a total number of coil windings of around 3 (each winding with 2 turns) and a total number of thermally conductive members of around 4. This arrangement is advantageous as it allows the windings to be cooled from both sides. The windings are connected to each other the make a continuous circuit. As such, there may be gaps in the thermally conductive members 120 to allow the conductor 110 to pass through the members 120.

[0064] The ends 132, 134 ofthe thermally conductive members 120 may be in thermal communication with one or more thermally conductive portions (not shown). The thermally conductive portions may receive thermal energy from the coil windings 110 and efficiently transfer the thermal energy from the coil 110 to the ends ofthe 132, 134 of the thermally conductive members 120. The ends 132, 134 may be therefore connected to a heat sink. These ends may be heat sunk to cryogenic temperatures. Heat from the coil layers 110 may be conducted to the ends 132, 134 towards the heat sinks.

[0065] Figure 2 shows a simple schematic of a portion 200 of an electrically driveable motor for use in an aircraft. The motor comprises a motor coil 210 comprising a plurality of coil windings. The motor comprises a plurality 220 of elongate thermally conductive members each arranged to thermally communicate with at least a portion of one of the plurality of coil windings.

[0066] The plurality of elongate thermally conductive members 220 are in a different structure to those shown in the example of in Figure 1. In the example of Figure 2, the thermally conductive members 220 are in the form of strips 221 or the like. While in Figure 1 , the thermally conductive members 120 are in the form of plates, thermally conductive members 220 of Figure 2 are in the form of strips 221. The strips 221 may be divided at a point across the centre shown by numeral 223.

[0067] Smaller plates may be advantageous by virtue of being easier and cheaper to manufacture over large single piece plates. In examples, using plates divided into a number of strips provides for a greater ease of manufacture and assembly.

[0068] In the arrangements herein, the thermally conductive members may be directly connected to the coil windings. This is a different approach to those taken previously, deeming direct connection to not be feasible due to expansion and contraction issues. The thermally conductive members may be made of ceramics or the like. It is not straightforward to connect ceramics to metal coil windings.

[0069] This connection would preferably not be via metallising the ends of the thermally conductive members to allow for soldering to the metal motor coils as this would introduce additional metal into the arrangement which would, as an electrical conductor, increase the presence of eddy currents which leads to additional thermal energy production. Eddy currents also lead to AC losses. These are undesirable in the present arrangements.

[0070] Rather, the connection may be formed via surface treatments. In examples, the thermally conductive members may be prepared for connection to a portion of at least one of the plurality of coil windings via at least one of laser ablation and a sol-gel process. These types of processes modify the surface of the thermally conductive members so that a bond can be made to the motor coil windings. This bond may be via epoxy or the like. Such approaches are highly suitable for the above-mentioned materials such as sapphire etc. As such, the processes of laser ablation and sol-gel enable the ceramic to be bonded to the motor coil via some further method (e.g. epoxy).

[0071] In contrast, the ends of the conductive members, that connect to the heat sinks of the thermally conductive portion(s), may be directly soldered or metallised and soldered or brazed or the like. These connections may introduce metal as there is little chance for disruptive AC losses or eddy current production to occur from the motor coils. Direct soldering is a feasible option using solders such as S-Bond™ Technologies “Active Solder”. A solder that reacts with the oxide surface to form a reliable joint may be used. Other suitable solder / flex combinations exist and may be used.

[0072] A suitable material for use in the present arrangement as the thermally conductive members includes sapphire. These may be sapphire plates or sapphire cables or the like. The thermal conductivity of the thermally conductive members in use is at least 100 Wnr’K'1and the electrical conductivity is less than 10’14Snrr1. “In use” here refers to the properties of the material at the operating temperature of the motor. The properties at room temperature or the like, may differ from those mentioned herein. “In use” therefore takes a meaning of during operation.

[0073] The thermally conductive member may be arranged to be in thermal communication with the motor coil windings as shown in the examples of Figures 1 and 2. The thermally conductive member may abut the motor coil windings. Abutting is suitable for thermal energy to be effectively transferred from the motor coil to the thermally conductive members. Connecting the thermally conductive members to the motor coil windings may be advantageous to provide a further level of resilience in the arrangement for maintaining a strong physical connection between the elements, to maintain a strong thermal conductivity between the elements, in response to thermal contraction and expansion.

[0074] The examples shown in Figures 1 and 2 show plate like thermally conductive members interleaved with portions of the motor coil. More complex arrangements are possible including winding cables into the motor coil to provide a more thorough intermixing of the thermally conductive members and the coil windings. A more thorough intermixing leads to decreased likelihood of hot spots and therefore an reduction in the damage that may occur therefrom. Forming cables from suitable materials is advantageous for the above reasons. In particular, cables may be formed from fibre optics single crystal sapphire structures. This may provide greater flexibility in the manufacture and assembly of the present electrically driveable motor.

[0075] The motor coil design may be around 200 mm long and 20 mm thick. The improved cooling from the arrangement herein improves the feasibility of longer coils or running coils with more common geometry at higher power. These allow production of a more powerful and / or compact motor.

[0076] Longer coils allows production of a motor with a lower overall diameter. The coil lengths may be around 600 to 1000 mm. The entire motor diameter may be less than 100 cm.

[0077] The thermally conductive members may connect to a heat sink at the ends (such as at ends 132, 134 of Figure 1). These heat sinks may be cooled by cryogenic material from a cryogen source or the like.

[0078] The cooling may be provided so that the coils of the motor may be maintained in a superconducting region. The cooling may be provided so that the coils of the motor may be maintained in a hyperconducting region. The coils may be of a high purity of material. The coils may be made of copper or aluminium or the like.

[0079] The thermally conductive portion may be a heat sink or the like for removing thermal energy from the thermally conductive members. The motor may have one or more thermally conductive portions. The motor may have two thermally conductive portions arranged at either end of the motor coil or the thermally conductive members. The plurality of thermally conductive members may connected to both thermally conductive portions. The thermally conductive portion may be a cold block or a large thermally conductive block that is connected to a cooling arrangement to remove thermal energy from the device. The thermally conductive portion may have a thermal mass of around 10 times or more of the thermal mass of a thermally conductive member. This allows the thermally conductive portion to effectively disperse thermal energy received from the thermally conductive members. The thermally conductive members are arranged to effectively transport thermal energy while the thermally conductive portion is arranged to store and disperse the thermal energy.

[0080] In particular, the electrically drivable motor may be used with a low temperature arrangement such as a superconducting motor arrangement or a motor with superconducting elements contained within it. Additionally, or alternatively, the motor may be used with a low temperature arrangement such as a hyperconducting motor arrangement or a motor with hyperconducting elements contained within it. Each of these motor arrangements may be operated using alternating current.

[0081] In an example, the plurality of thermally conductive members are elongate and have a diameter of around 0.1 mm or greater. The diameter of a thermally conductive member may be around 0.1 mm or greater.

[0082] The motor coil may be formed of materials such as niobium-titanium, high temperature superconductor, or magnesium diboride. Such options offer utilising superconducting properties wherein electrical resistance of effectively zero can provide extremely high electrical efficiencies. Such materials however have relatively low thermal conductivity. As such, these materials may be advantageously used in cryogenic alternating current motors for the motor coils.

[0083] The cryogen source discussed herein may be a source of liquid helium or liquid hydrogen or the like. The cryogen may be provided as a liquid or a gas to the conduits for use in thermal energy removal.

[0084] The term “cryogen” is used to refer to the actual substance that is of a cryogenic temperature. Such a substance would in most arrangements be contained within a tank or container or the like. A cryogenic temperature clearly depends on the substance in question however cryogenic behaviour has been observed in substances up to -50°C. Therefore, cryogenic temperature is taken herein to refer to temperatures below -50°C. The cryogen may be any of hydrogen, helium, nitrogen or the like, in liquid, gas or supercritical phase. The cryogen may be helium that is cooled to a very low temperature without being liquefied. Such a cryogen is particularly suitable for use in an aircraft. In an example, the cryogen may be frozen nitrogen or cryogenically frozen water.

[0085] In an example, at least a portion of the plurality of thermally conductive members is arranged into a cable for example by winding. The winding may be a spiral or helical winding. Such an arrangement allows individual strands in the cable to transition from being centrally arranged in the cable to being outwardly arranged in the cable. In this way, each strand can contribute more effectively to the overall cooling of the motor coil. In an example, the device is arranged in use so that each of the second plurality of thermally conductive members experiences an extremely low power of heating due to eddy currents. In comparison cables in modern state of the art systems produce about 10 Watts of excess power that is converted into heating, in the presently disclosed arrangement cables produce about 0.1 Watts of excess power. This is therefore a clear significant improvement.

[0086] Modern arrangements that have been found to provide around 10 Watts include an arrangement utilising slotted aluminium in place of the plurality of thermally conductive members or the like.

[0087] The present arrangement therefore, provides a system that can reduce undesirable heating by a factor of around 100. This improves the overall performance of the device in particular in handling the removal of thermal energy and not producing undesirable additional heating for conducting away from the device.

[0088] In an example, the plurality of thermally conductive members may be bonded to the coil surfaces of the motor coil. This bonding ensures strong physical connection between the elements and therefore improves thermal conductivity between the two elements. This bonding may be epoxy impregnated or the like.

[0089] The motor may be held at low temperatures using, e.g., cryogens. The cryogen present for use with fuel cells or the like in the electrical motor may be used for cooling the thermally conductive portion in the arrangement herein. This advantageously utilises an already present feature for a secondary aspect in the device of the present invention.

[0090] Referring now to Figure 3, there is shown a schematic view of a portion 300 of an electrically driveable motor for use in an aircraft according to examples. The portion 300 shares a number of features in common with Figures 1 and 2. Similar numerals are used to those Figures with number increased by 200 and 100 respectively. For example, portion 100 of Figure 1 is similar to portion 200 of Figure 2 and portion 300 of Figure 3. Not all similar features will be discussed in detail.

[0091] The portion 300 comprises a motor coil 310 comprising a plurality of coil windings. The motor comprises a plurality of elongate thermally conductive members 320 each arranged to thermally communicate with at least a portion of one of the plurality of coil windings 310. In the example of Figure 3, there are coil layers and coil end portions 336, 337 shown. The coil 310 has a current in portion 337 and a current out portion 336 at ends 334, 332 of the portion 300. As noted above, the portion 300 may be cooled from the ends 332, 334 via any suitable mechanism such as connection to a heat sink. The current in 337 and out 336 portions can be at any end 332, 334 of the portion 300.

[0092] The elongate thermally conductive members 320 are in the form of plates. The plates have considerable length and widths but a much smaller depth. There are seven thermally conductive members per layer in the example of Figure 3. The thermally conductive members are interleaved with the coil layers. A coil layer may be described as abutting on either side a thermally conductive member. Specifically, the arrangement of Figure 3 is an A-B-A-B-A arrangement wherein the thermally conductive members are arranged either side of a coil layer.

[0093] The arrangement of Figure 3 has a gap 323 in the thermally conductive members 320. The gap 323 is useful to allow the coil 310 to move between layers of the thermally conductive members 320. The gap 323 is also useful towards a midpoint of the coil (line of symmetry). This allows for smaller plates to be used which provides a cheaper arrangement.

[0094] The arrangement of Figure 3 illustrate joggles 339 in the motor coil 310. The motor coil 310 moves through layers as it progresses. These portions as to where the motor coil 310 moves layer are referred to a joggles 339. This allows the motor coil to form a complete coil. The joggles may be located anywhere along the coil. This may be towards the ends 332, 334 of the arrangement or towards the centre of the arrangement shown.

[0095] There are gaps 323 in the heat shunts to allow for the joggles 339.

[0096] Referring now to Figure 4, there is shown a schematic view of a portion 400 of an electrically driveable motor for use in an aircraft according to examples. The portion 400 of Figure 4 shares a number of features with portion 300 of Figure 3 with numerals for elements with functions that are the same or similar increased by 100. Not all elements will be discussed in detail.

[0097] The portion 400 has a coil 410 and thermally conductive members 420. The thermally conductive members 420 are in the form of cables of ceramic strands. This may allow for different arrangements of the portion 400 to be formed in comparison to the thermally conductive members 420 being arranged in a plate form or the like. Cables are advantageous as being easier to assemble and more robust (less likely to be damaged). Cables may more easily account for thermal contraction and expansion during use than plates.

[0098] Referring now to Figure 5, there is shown a schematic view of a portion 500 of an electrically driveable motor for use in an aircraft according to examples. The portion 500 shows a structure combining a motor coil and thermally conductive members. The arrangement 500 shows a structure with motor coil conductor and ceramic filaments cabled together 555. The motor coil may be formed of aluminium or copper with electrical isolation. This may be in the form of litz wires or the like.

[0099] The arrangement shown has a current in portion 537 and a current out portion 536. The arrangement 500 has electrically conducting links 556 between the terminals connecting to all the windings to form a coil. The terminals shown (in grey) at the end of the cables may be formed on either end of each winding. The terminals may be cooled to maintain ceramic strands cool and therefore maintain the entire coil 555 as cool.

[0100] The arrangement of Figure 5 therefore has co-cabling for the coil windings and the thermally conductive members. This may be sapphire filaments or the like and aluminium litz wires. These may be cabled together on a strand basis in which case the windings and the members are in very close contact (on a more micro scale). Alternatively, a more macro approach could be taken whereby the arrangement is in effect a cable of cables. This may be that small cables of motor windings and small cables of thermally conductive members are woven together. This cable of cables (macro) approach may be easier and cheaper however the strand basis (micro) would provide greater contact and therefore greater and more homogenous thermal removal.

[0101] The cooling discussed above may be provided by heat sinks at ends of the motor coil. Such sinks may be located in low current field regions to minimise eddy currents. The blocks may provide terminus points for cables or cables of cables as per the above. This allows for connecting the blocks to be controlled to provide a suitable current transfer from coil to coil. Blocks may be cooled by helium or other cryogenic or low temperature material.

[0102] Although the invention described herein relates to thermal energy transfer for an electric motor in particular in the example of such a motor in an aircraft, it may also be applied to application where propulsion generation involves generating undesirable heat that is to be transferred away from the point of generation. These applications may include automotive, space, domestic or commercial propulsion generation and so forth.

[0103] The system herein is simple to manufacture, robust against physical change such as during temperature conduction, and highly effective. The system herein is an improvement over present state of the art systems.

[0104] The thermally conductive members may be manufactured via additive manufacturing to provide particularly narrow conductive elements interlaced with insulating portions.

[0105] Materials such as sapphire, diamond, aluminium nitride, and beryllium oxide have been shown to be highly effective in providing high thermal conductivity with very low electrical conductivity.

[0106] Suitable here may mean suitable for rapid thermal conductivity from the coil. In particular, monocrystalline sapphire has a thermal conductivity of over 104Wnr’K’1below 50 K. Such cooling is feasible with cooling from cryogens and the like as discussed above.

[0107] Polycrystalline sapphire has been found to be stronger and therefore more reliable under stress. Use of polycrystalline may increase the lifetime of the system. Polycrystalline is also cheaper and therefore use improves the overall device from a manufacturing cost perspective.

[0108] Other options include beryllium oxide which may be grown in a crystalline form to occupy a shape desirable for use in the system. As noted above, there is not requirement for these materials to be formed in strands and therefore blocks will suffice.

[0109] As such, disclosed herein is a proposed device wherein non-typical materials are manipulated for their properties and use in a thermal and electrical environment. Typical devices do not use these materials however the inventors have designed a system that overcomes the inherent drawbacks of these materials to enable a highly effective overall function.

[0110] The device herein has excellent thermal energy transfer and provides little to no eddy currents. Therefore the overall efficiency of the cooling system for use in an electrically operated aircraft (electrically operated in terms of at least some propulsion is offered via electrical energy generation) is significantly improved over previous arrangements.

Claims

CLAIMS1 . An electrically drivable motor for use in an aircraft, the motor comprising: a motor coil comprising a plurality of coil windings; a plurality of elongate thermally conductive members each arranged to thermally communicate with at least a portion of one of the plurality of coil windings; at least one thermally conductive portion arranged to thermally communicate with a plurality of elongate thermally conductive members, wherein a portion of at least one of the plurality of elongate thermally conductive members abuts a portion of at least one of the plurality of coil windings; and wherein each of the plurality of elongate thermally conductive members has an in use thermal conductivity of at least 100 Wnr’K'1and an electrical conductivity of less than 10-14Sm-1.

2. The electrically drivable motor of claim 1 , wherein a portion of at least one of the plurality of elongate thermally conductive members is connected to a portion of at least one of the plurality of coil windings.

3. The electrically drivable motor of claim 2, wherein a portion of at least one of the plurality of elongate thermally conductive members is connected to a portion of at least one of the plurality of coil windings via at least one of laser ablation and a sol-gel process.

4. The electrically drivable motor of any preceding claim, wherein the plurality of elongate thermally conductive members are in the form of plates.

5. The electrically drivable motor of any preceding claim, wherein the plurality of elongate thermally conductive members are interleaved with the plurality of coil windings.

6. The electrically drivable motor of any of claims 1-3, wherein the plurality of elongate thermally conductive members are in the form of cables.

7. The electrically drivable motor of claim 6, wherein the plurality of elongate thermally conductive members are intermixed with the plurality of coil windings.

8. The electrically drivable motor of claim 7, wherein the plurality of elongate thermally conductive members are evenly intermixed with the plurality of coil windings throughout a full length of the plurality of coil windings.

9. The electrically drivable motor of claim 8, wherein the plurality of elongate thermally conductive members are wound into the plurality of coil windings.

10. The electrically drivable motor of any preceding claim, wherein the plurality of coil windings has a length in a first axis of at least 20 cm.

11. The electrically drivable motor of any preceding claim, wherein the motor coil has a length in a second axis of no more than 20 cm.

12. The electrically drivable motor of any preceding claim, wherein the plurality of elongate thermally conductive members are formed from at least one of: single crystal sapphire; polycrystalline sapphire; amorphous sapphire; diamond; aluminium nitride; alumina; and, beryllium oxide.

13. The electrically drivable motor of any preceding claim, wherein at least one thermally conductive portion is formed from at least one of: single crystal sapphire; polycrystalline sapphire; amorphous sapphire; diamond; aluminium nitride; aluminium; copper; and, beryllium oxide.

14. The electrically drivable motor of any preceding claim, wherein the plurality of elongate thermally conductive members are connected to the at least one thermally conductive portion via at least one of brazing, soldering, and metallising and soldering.

15. A propulsion system for an aircraft comprising: a cryogen source containing a cryogen for use in electrical energy generation; at least one fuel cell for generating electrical energy at least in part from the cryogen; the electrically drivable motor of any of claims 1 to 14; the at least one fuel cell arranged to provide electrical energy to the electrically drivable motor.

16. The propulsion system of claim 15, wherein the at least one thermally conductive portion and the plurality of elongate thermally conductive members are in thermal communication with the cryogen, the cryogen arranged to provide a heat exchanger function to at least one of: the at least one thermally conductive portion; and, the plurality of elongate thermally conductive members.

17. The propulsion system of claims 15 or 16, wherein the at least one thermally conductive portion comprises a conduit for carrying a fluid, wherein the conduit is in fluid communication with the cryogen in the cryogen source, and wherein in use a fluid cryogen from the cryogen source is arranged to be provided to the conduit and is arranged to flow through the conduit.

18. An aircraft comprising the electrically drivable motor of any of claims 1 to 14 or the propulsion system of any of claims 15 to 17.

19. A method of operating the electrically drivable motor of any of claims 1 to 14, the propulsion system of any of claims 15 to 17 or the aircraft of claim 18.

20. A stator cooling arrangement comprising the electrically drivable motor of any of claims 1 to 14.

21. The stator cooling arrangement of claim 20, further comprising a gas cooling arrangement for providing gas cooling to a stator.

Images