Description

The present invention relates to a multi-staged axial compressor propulsion motor for an electric propulsion aircraft.

It has been known to use one-stage compressors as propulsion means for aircraft, for example in the form of so-called “ducted fans”, in which a compressor stage with a plurality of blades is driven to rotate within a cylindrical housing in order to create thrust along its longitudinal axis.

During operation of such compressors, due to the geometrical shape and rotating movement of the single stage of blades, a cross-flow and a parasitic transverse impulse is created by the compressor stage. Thus, in known one-stage compressors of the above described kind, in addition to the desired impulse in the longitudinal direction, its single compressor stage also produces a parasitic transverse impulse in the driven air stream due to the rotation of its blades, which is noticeable as a twist in the discharge air stream. Thus, in order to guide the resulting airflow in a suitable manner in the longitudinal direction and avoid the formation of cross-flows, stator or guide vanes have to be installed downstream of the compressor stage inside the housing in the direction of the driven airflow acting as baffle plates.

However, the installation of such static guide elements within the compressor housing and thus in the driven airflow necessarily leads to losses generated during its operation as the transverse impulse component is absorbed in the stator vanes. In other words, by balancing out said twist of the produced airflow by means of static elements therein, the relative thrust in the longitudinal direction and thus the efficiency of the compressor is reduced. Also, the guide vanes representing lossy flow obstacles in the airflow can only be designed for a specific load point due to their static nature and could only be dynamically adapted for a larger load range with much increased complexity and thus cost, while their static nature on the other hand further decreases the efficiency of the compressor over a wide range of operational parameters.

It is therefore the object of the present invention to provide an improved axial compressor propulsion motor for an electrical propulsion aircraft, in which the drawbacks of the prior art discussed above are overcome.

For this purpose a multi-staged axial compressor propulsion motor is proposed, comprising a housing, defining a substantially cylindrical inner space and a longitudinal axis, at least two compressor stages arranged in the inner space of the housing in a rotatable manner one behind the other along the longitudinal axis, wherein each compressor stage comprises an inner blade ring and an outer blade ring with a plurality of blades extending between the inner and outer blade rings, and an electrical drive assembly adapted to drive at least two of the compressor stages in a counter-rotating manner.

Thus, in the axial compressor propulsion motor according to the present invention, at least two counter-rotating compressor stages are arranged one behind the other and electrically driven in a counter-rotating manner. This design allows to adapt the two or more axial compressor stages concerning their geometrical and propulsion properties in such a way that the angular momentum induced in the air stream by the rotation of the individual compressor stages is zero or close to zero at the outlet of the last compressor stage. This makes a guide vane ring or other static elements within the airflow inside the housing obsolete and eliminates the frictional losses of static elements such as guide vane rings. Furthermore, the overall efficiency of the propulsion motor is further improved as the second and further compressor stages are operating at an already increased air-pressure level due to the pre-compression provided by the at least one compressor stage positioned upstream in the airflow direction. In some possible embodiments of the present invention, the blades of the at least two compressor stages may be tilted or bent with respect to the longitudinal axis of the housing in opposite directions. By adapting this feature, the noise level created during operation of the propulsion motor can be reduced, since the area of maximum convergence between two counter-rotating rotor blades can be vastly reduced from a more or less line-shaped segment along the radial direction of the individual pairs of blades of the compressor stages when approaching each other to a more point-like area traveling along the radial blade length while the two blades pass each other during counter-rotation. Thus, a siren effect of two rotor blades meeting each other as well as possible compression shocks can be reduced, resulting in a substantial reduction of noise created during operation of the propulsion motor. While different shapes and designs of such tilted blades are conceivable, said blades may for example be sickle-shaped or inclined with respect to one another.

While the concrete layout of the individual compressor stages concerning the arrangement of the blades can be chosen according to various boundary conditions, such as desired thrust and correspondingly required rotations per minute of the compressor stages of the propulsion motor, while achieving a uniform airflow with a thrust direction along the longitudinal axis of the housing, in some embodiments, the at least two compressor stages may be provided with an identical number of blades and/or the blades of the at least two compressor stages may be tilted with respect to the longitudinal axis by the same amount. By adapting the compressor stages in such a manner, a high degree of symmetry between the stages is achieved which facilitates construction and operation of the propulsion motor and reduces asymmetrical effects such as torques or forces acting in an undesired manner.

In order to further improve the airflow within the housing and further eliminate static or quasi-static elements therein, the outer blade ring of at least one of the compressor stages may be aligned with a cylindrical inner wall surface of the housing. Thus, the corresponding outer blade ring is embedded in a respective slot or recession of the inner wall of the cylindrical housing and its aerodynamic resistance is minimized.

In this context, a hub section may be centrally arranged in a fixed manner in the inner space of the housing, and it is furthermore conceivable to centrally support at least two, preferably all, of the compressor stages in the hub section by means of respective bearing assemblies .

Alternatively, a first compressor stage may be supported on its radially outer side on the housing by means of a first bearing assembly, and a second compressor stage may be supported on its radial inner side by means of a second bearing assembly, preferably within the hub section. Such an embodiment, in which at least one of the compressor stages is supported on its radial outside while at least one other compressor stage is supported on its radial inside can be beneficial concerning the installation space needed for the respective bearings and provides for what is often referred to as a floating support of the second compressor stage.

In one particular specific embodiment of the axial compressor propulsion motor as just described the outer blade ring of the first compressor stage may be supported on the housing by means of the first bearing assembly and the second compressor stage may comprise an inner axle section, preferably extending within the hub section, wherein the second bearing assembly is provided to support the inner axle section on the first compressor stage. Thus, said floating arrangement of the compressor stages is achieved which on the one hand further minimizes static elements positioned in the airflow path within the housing thus reducing aerodynamic drag, while on the other hand, frictional losses may also be reduced in the bearing assemblies.

In another specific embodiment, the outer blade ring of the first compressor stage may be supported on the housing by means of the first bearing assembly, and the first compressor stage may further comprise a radially inner axle section, preferably extending within the hub section, wherein the second bearing assembly may be supported on the inner axle section of the first compressor stage by means of the second bearing assembly. Thus, according to the present invention, the second bearing assembly may be assigned to either the first compressor stage which itself is supported on the housing by means of the first bearing assembly, or to the second compressor stage, while the respective other compressor stage is then provided with the axle section to be supported on the second bearing assembly.

In order to reduce the constructive effort and number of parts required for driving the at least two compressor stages in a counter-rotating manner, the electrical drive assembly may comprises a single static excitation arrangement, which is adapted to be energized in such a manner that at least two of the compressor stages are driven in a counter-rotating manner. Therein, the term “static” relates to the fact that said excitation arrangement is provided to the propulsion motor according to the present invention in such a manner that it is immovable with respect to the motor housing.

In this context, different types and layouts of single static excitation arrangements may be employed. For example, said excitation arrangement may be formed by a rectifier circuit driving individual motors for the compressor stages with junctioned coils at reversed winding sense. In such designs and assuming that two compressor stages are employed, said motors may either both be of the synchronous motor type or one may be of the synchronous motor type while the other one may be of the asynchronous motor type.

In another embodiment, the single static excitation arrangement may comprise an electromagnet assembly positioned adjacent to one of the compressor stages comprising a coil and drive electronics, which are arranged to provide the coil with an electric current in order to induce an alternating magnetic field, and the propulsion motor may further comprise a magnetically excitable commutator part, which is provided to one of the compressor stages, and a permanent magnet part, which is provided to another one of the compressor stages. In such embodiments, by suitably driving the coil, an uninterrupted transmission of the drive magnetic field from the excitation arrangement to the commutator part and thus the permanent magnet part is achieved, driving the commutator part and the permanent magnet part in different directions.

In this context, a first compressor stage in its outer blade ring may be provided with at least two pairs of permanent magnets, each pair arranged in opposite magnetic direction, thus forming the permanent magnet part, in order to provide for the possibility to electrically drive said compressor stage by means of alternating magnetic fields produced by a suitable electro-magnet arrangement in the proximity thereof.

Furthermore, a second compressor stage in its outer blade ring may be provided with two radial layers of magnetically excitable material, in particular ferritic material, thus forming the magnetically excitable commutator part, wherein each of the two radial layers preferably forms a flush rear face in the longitudinal direction, and each layer forms at least two tabs opposite the rear face, thus facing the first compressor stage.

In such embodiments, a gap may be formed in the second compressor stage between the two radial layers of magnetically excitable material in order to allow an improved cooling of active components of the propulsion motor by means of air flowing or being led through said gap.

As a means to drive the at least two compressor stages in a counter-rotating manner, the electro-magnet assembly may be positioned adjacent to the second compressor stage, wherein the coil is formed with a two-sided armature, wherein each of the sides faces a respective one of the two radial layers of the second compressor stage, and the drive electronics are arranged to provide the coil with an electric current in order to induce an alternating magnetic field in the armature for driving the second compressor stage in rotation.

Thus, a floating, counter-rotating electrical motor to drive the two compressor stages by the rotationally symmetrical induction of the magnetic field into the ferritic layers of the second compressor stage may be achieved, which reduces the complexity of the motor as well as of the drive electronics. In this context, said drive electronics may for example comprise a H-bridge switching assembly for selectively energizing the coil in such an embodiment.

In order to make optimal use of the space available in the propulsion motor according to the invention, the drive electronics may at least partially be integrated in the housing, which can also contribute to facilitating their cooling due to compressed air flowing in their vicinity during operation of the motor as well as outside the housing during flight of the aircraft.

Furthermore, the propulsion motor according to the invention may further comprise a positioning sensor system adapted to periodically determine the angular position and/or angular velocity of at least one of the compressor stages, preferably each compressor stage, such that the positions of the permanent magnets relative to one another may be evaluated and feedback may be provided to the drive electronics for achieving optimal efficiency and operating conditions of the drive electronics as well as overall motor at all times.

In order to improve and facilitate cooling of active components of the propulsion motor according to the present invention, at least some of the blades of at least one of the compressor stages may be provided with internal air ducts extending towards a radially outer side. By providing such radially extending air-guiding means, a constant overpressure airflow for cooling motor components is provided in a radial direction and the outer ring blade of the compressor may be guided on an air film. Furthermore, this design choice helps preventing dust or other particles from ingressing through the gaps between the outer blade rings of the compressors and/or the housing components.

According to a second aspect, the present invention relates to an aircraft with a fuselage and at least one pair of wings, further provided with at least one multistaged compressor propulsion motor according to the present invention, wherein the at least one multi-staged compressor propulsion motor may be integrated with a flap element, which is pivotably mounted to one of the wings. Such a design of an electrical propulsion aircraft offers high efficiency combined with advanced control features, in particular since the prevention of transverse impulse components of the propulsion motors according to the invention facilitates the pivoting of such flaps with respect to the wings and/or fuselage of the aircraft.

Further features and advantages of the present invention will become even clearer from the following description of an embodiment thereof, when taken together with the accompanying drawing, which in particular illustrate:

Fig. 1 a schematic view visualizing the working principle of a propulsion motor according to the present invention;

Fig. 2 a schematic cross-sectional view of an embodiment of the propulsion motor according to the present invention;

Fig. 3 a cross-sectional view along the plane denoted A-A in Fig. 2;

Fig. 4 a cross-sectional view along the plane denoted B-B in Fig. 2;

Fig. 5 a cross-sectional view along the plane denoted C-C in Fig. 2;

Fig. 6 a front view of the blades of one of the compressor stages shown in

Fig. 2;

Figs. 7 and 8 schematic cross-sectional views of alternative variants with different bearing arrangements; and

Figs. 9 and 10 schematic cross-sectional views of alternative variants with different propulsion arrangements.

In Fig. 1 , a multi-staged axial compressor propulsion motor according to the present invention is shown in a schematic manner for visualizing its working principle and generally denoted by reference numeral 10. The propulsion motor 10 comprises a first compressor stage 12 and a second compressor stage 14, which are each provided with a plurality of blades 12a and 14a, respectively. By driving the two compressor stages 12 and 14 in a counterrotating manner, the individual thrust components T12 and T14 provided by the respective compressor stages 12 and 14 add up in such a manner that an overall thrust T is produced, in which all components directed perpendicularly to the longitudinal direction L of the propulsion motor 10 are substantially canceled out.

Thus, by operating the propulsion motor with its two compressor stages 12 and 14 rotating in two opposite directions, unwanted cross-flows produced by each individual compressor stage 12 and 14 can be compensated for without the use of static guide vanes which would increase aerodynamic drag and reduce the overall efficiency of the propulsion motor 12. Hence, by automatically compensating for the internal cross-flows of the compressor stages 12 and 14, a highly efficient propulsion motor can be provided, in which due to its symmetrical design, torque and momentum perpendicular to its longitudinal direction R and direction of thrust can be minimized.

Fig. 2 shows a schematic cross-section view of the propulsion motor 10 in which further components are shown. In particular, the propulsion motor 10 comprises a housing 16 with a substantially cylindrical inner space 16a around the longitudinal axis L. Said inner space 16a serves as a flow duct for the air to be compressed by the compressor stages 12 and 14, such that the propulsion motor 10 is of the ducted-fan type.

Furthermore, the propulsion motor 10 according to the present invention comprises a hub section 18, which is centrally arranged in a fixed manner in the inner space 16a of the housing 16. It can furthermore be seen in Fig. 2 that each of the two compressor stages 12 and 14 in addition to its blades 12a and 14a extending along a radial direction R also comprises an inner blade ring 12b, 14b, as well as an outer blade ring 12c, 14c, respectively. Said outer blade rings 12c, 14c are aligned with the cylindrical inner wall surface of the housing 14, such that the outer blade rings 12c and 14c are accommodated in a recession 16b of the housing.

Furthermore, it is shown in Fig. 2 that the outer blade ring 12c of the first compressor stage 12 is supported on the housing 16 by means of a first bearing assembly 20a and that the second compressor stage 14 comprises an inner axle section 22 extending within the hub section 18, while additionally a second bearing assembly 20b is provided, supporting the inner axle section 22 on the first compressor stage 12. Thus, a floating arrangement of the two compressor stages 12 and 14 is achieved, which reduces friction losses and facilitates its electrical operation as will be discussed further below.

Referring back to Fig. 2, said figure furthermore shows an electrical drive assembly 24 positioned adjacent to the second compressor stage 14 and comprising a coil 24a with a two-sided armature, as well as drive electronics 24b, which are shown only schematically but may for example comprise an H-bridge switching assembly for selectively energizing the coil 24a. In order to be able to establish a control method for the operation of the drive electronics 24b, the propulsion motor 10 further comprises a positioning sensor system 32 adapted to periodically determine the angular position and/or angular velocity of each compressor stage 12, 14, and which is coupled to the drive electronics 24b to provide corresponding data.

Reference shall now be made to Figs. 3 to 5, which show the outer blade rings 12c and 14c as well as the electro-magnet 24a in respective cross-sectional views along the planes A-A, B-B and C-C denoted in Fig. 2, respectively.

In Fig. 3, the outer blade ring 12c of the first compressor stage 12 is shown to comprise two pairs of permanent magnets 26, wherein each pair is arranged in an opposite magnetic direction.

In contrast, Fig. 4 shows the outer blade ring 14c of the second compressor stage 14, which is provided with two radial layers 28a and 28b of ferritic material with permanent-magnet properties, stapled in a radial direction of the compressor stage 14, with a gap 28c formed there between. Each of the two radial layers 28a and 28b forms a flush rear end face in the longitudinal direction R and each layer forms at least two tabs opposite its rear face, thus facing the first compressor stage, as can be seen in Fig. 2.

Fig. 5 now shows the radially arranged electromagnet 24a adjacent to the back of the second compressor stage 14 in the longitudinal direction R with its two-sided armature, wherein each of the sides faces a respective one of the two radial layers 28a and 28b of the second compressor stage 14 as just discussed in the context of Fig. 4. As denoted by “N/S” in Fig. 4, depending on the current flowing through the electromagnet at a given time, a corresponding magnetic field is produced therein. Thus, by means of the drive electronics 24b, the radially arranged electromagnet 24a provides a rotationally symmetrical induction of the magnetic field into the ferritic layers 28a and 28b of the second compressor stage 14, independent from the rotational position of said compressor stage 14, thus allowing an electrically driven rotation of the first and second compressor stages 12 and 14 in a counter-rotating manner.

Lastly, reference shall be made to Fig. 6, which in a front view shows the blades 12a of the first compressor stage 12 as well as a single blade 14a of the second compressor stage 14, from which it becomes obvious that the blades 12a and 14a are tilted with respect to the longitudinal axis R in opposite directions and are sickle-shaped or inclined.

As can be seen in Fig. 6, the region of overlap 30 between the blade 12a of the first compressor stage 12 and blade 14a of the second compressor stage 14 is reduced as compared to possible embodiments in which the blades are extending straight in the radial direction R. Thus, the region of overlap 30 between the two rotor blades 12a and 14a during their counter-rotating movement travels along the blade length, while the two blades pass each other. Thus, a siren effect or compressor shocks during operation of the propulsion motor 10 may be reduced, such that the operation thereof will produce less noise than the briefly mentioned possible embodiment with blades extending straight in the radial direction R.

With respect to the embodiment of a multi-staged axial compressor propulsion motor shown in Fig. 2, it shall in the following be discussed that both concerning the arrangement of the bearing assemblies for the first and second compressor stages as well as for the propulsion arrangement, alternative approaches are possible. For this purpose, in Figs. 7 and 8, variants different placements of bearing arrangements are shown which may be employed instead of the bearing arrangements in the embodiment of Fig. 2, while in Figs. 9 and 10 variants of propulsion arrangements are shown, which may be employed instead of the corresponding propulsion arrangement of Fig. 2. The respective figures have been simplified for easier understanding of the illustrated inventive principles in that certain components have been omitted.

It shall also be stated that any of the bearing arrangements and propulsion arrangements of Fig. 2 and Fig. 7 to 10 are freely combinable in further possible embodiments of the present invention. It shall further be pointed out that the respective variants of propulsion motors of Fig. 7 to 10 are denoted with reference numerals 100, 200, 300 and 400, respectively, and that components identical or similar to corresponding components of propulsion motor 10 of Fig. 2 have been denoted with the same reference numerals to which corresponding multiples of 100 has been added. The additional variants of Fig. 7 to 10 will in the following only be describes concerning their differences to the embodiment of Fig. 2 and for a detailed discussion of the remaining components, reference shall be made to the description of Fig. 2 above.

In Figs. 7 and 8, alternative variants of the placement of the respective bearing assemblies 120a, 120b and 220a, 220b are shown. While in the embodiment of Fig. 2, the respective bearing assemblies 20a and 20b are both assigned to the first compressor stage 12, in that said first compressor stage 12 is supported on the housing 16 by means of the first bearing assembly 20a and carries the second bearing assembly 20b on which the second compressor stage 14 is supported by means of the inner axle section 22, in the embodiment of Fig. 7, the placement of the bearing assemblies 120a and 120b is slightly modified. In particular, while the first compressor stage 112 is still supported on the housing 116 by means of the first bearing assembly 120a, however, in this variant the inner axle section 122 is assigned to the first compressor stage 112, while the second compressor stage 114 is provided with the second bearing assembly 120b which supports the inner axle section 122. Thus, while the second compressor stage 114 is still mounted in a floating manner, the specific placement of the bearing assemblies 120a, 120b is slightly modified compared to the bearing assemblies 20a, 20b of the embodiment shown in Fig. 2. It shall also be pointed out, that in addition to the variants shown in Figs. 2 and 7, the second compressor stage 114 may be supported on the housing while the first compressor stage 112 would then be arranged in a floating manner, such that in total four different placement configurations of the corresponding bearing assemblies are conceivable in similar variants of the present invention.

In contrast, in Fig. 8 a variant of the propulsion motor of Fig. 2 is shown, in which both compressor stages 212 and 214 are supported by means of respective bearing assemblies 220a, 220b, both of which are positioned within the hub section 218. Thus, none of the compressor stages 212, 214 is arranged in a floating manner and Fig. 8 also shows hub supports 218a by means of which the hub section 218 is carried on and inside the housing 216.

Furthermore, in Fig. 9 a variant of the embodiment of Fig. 2 is shown, in which the electrical drive assembly 324 comprises a single rectifier circuit 324a acting as a single static excitation arrangement by driving two individual motors 325a, 325b for the respective first and second compressor stages 312, 314. As can be seen in the lower part of Fig. 9 in an enlarged view, in order to drive the two compressor stages 312 and 314 in different directions, the motors 325a and 325b comprise junctioned coils with reversed winding senses thus forming an “8” configuration. Therein, the outer respective outer blade rings 312a, 314a of the first and second compressor stages 312, 314 are each provided with permanent magnets such that said motors 325a, 325b may either both be of the synchronous motor type or one may be of the synchronous motor type while the other one may be of the asynchronous motor type, depending of the specific layout of the motors, their drive arrangement and the permanent magnets.

Finally, in Fig. 10 a further variant of the embodiment of Fig. 2 is shown in two views including a cross-section view along the plane A-A, in which the electrical drive assembly 424 similarly comprises an excitable coil 424a and corresponding drive electronics 424b. In contrast to the embodiment shown in Fig. 2, the magnetically excitable commutator part 426 assigned to the second compressor stage 414 is provided in the shape of two half-shells with different diameter, both of which are fixed to the outer blade ring 414a of the second compressor stage 414 and surround the coil 424a. Furthermore, the first compressor stage is provided with a permanent magnet part 428 on its outer blade ring 412a, which is equally positioned between the two half-shells of the commutator part 426. By energizing the coil 424a situated between the two half-shells, the second compressor stage is driven in rotation in a first direction while by controlling the magnetic field produced by the coil 424a in a suitable manner and thus correspondingly exciting the commutator part 426, the permanent magnet part 428 can be driven in the opposite direction such that the two compressor stages 412, 414 are driven in opposite directions.