Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K17/00—Asynchronous induction motors; Asynchronous induction generators
  • H02K17/02—Asynchronous induction motors
  • H02K17/16—Asynchronous induction motors having rotors with internally short-circuited windings, e.g. cage rotors
  • H02K17/20—Asynchronous induction motors having rotors with internally short-circuited windings, e.g. cage rotors having deep-bar rotors

Definitions

• the invention relates to an axial flux induction electrical machine as defined in the preamble of claim 1.
• the invention is chiefly developed to function as a motor, but also different generator embodiments may come into question.
• An axial flux machine as such is not by nature very well applicable as a high-speed induction machine, because the characteristics of an induction machine are usually the best when there are only few poles (two, or four at the maximum) in the machine.
• a two-pole solution is often unsuitable for an axial flux machine, because the arrangement of the end-winding of the stator winding is not often a functional solution in a two-pole machine. Therefore, also a high-speed axial flux machine has usually to be designed at least as a four-pole configuration. In that case, both the magnetic flux in the stator yoke and the current of the machine in the windings have to flow a quarter of the inner and outer peripheries of the machine tangentially without producing torque.
• the disc-like rotor frame comprises one or a plurality of circular plates, which have been machined of work-hardened metal sheet, such as rolled or otherwise work-hardened aluminium alloy sheet.
• the electrical conductivity of a sheet of this kind is good, being for instance as near as possible to that of pure aluminium, 35 MS/m, and usually varying between 15-28 MS/m, and its relative permeability being ⁇ 1.
• the appropriate aluminium alloys are both durable and have a good electrical conductivity. Pure aluminium conducts electricity better than aluminium alloys, but it is mechanically weak, and therefore its application in high-speed machines cannot be justified.
• the object of the invention in particular is to introduce a novel axial flux induction machine, which enables to improve the efficiency of the machine by several percentage units even up to or above 95%. Further, the object of the invention is, along with the improved efficiency, to increase the maximum rotation speed and power of the machine as well as to prevent excessive heating of the machine .
• the axial flux induction electrical machine of the invention is characterized in what will be presented in claim 1.
• An axial flux induction machine of the invention comprises a frame, a shaft bearing-mounted to the frame, a disc-like rotor supported by the shaft, and a stator comprising a stator winding and supported by the frame on the first side of the rotor in axial direction.
• the disc-like rotor comprises a circular, non-ferromagnetic rotor frame having an essentially uniform thickness, fabricated of a material with a high electrical conductivity, the rotor frame comprising uniform inner and outer peripheries and conductor bars fabricated of the same material, the conductor bars galvanically connecting the inner and outer peripheries, and the conductor bars together with the inner and outer peripheries forming in addition to the rotor frame also the cage winding of the rotor.
• each ferromagnetic piece has a surface plate on the surface against the stator, the resistivity of this surface plate being essentially higher than the resistivity of the ferromagnetic piece.
• ferromagnetic material can additionally be used as a load-bearing structure, in other words, a ferromagnetic element is arranged beside the non-ferromagnetic rotor frame on the opposite side of the stator.
• the resistivity of commonly used ferromagnetic elements is of the order of 0.1 ⁇ m, and thus the resistivity of the surface plate is appropriately above 0.2 ⁇ m.
• the resistivity of the surface plate is preferably between 0.3 and 1.5 ⁇ m.
• the material of the surface place may be selected individually for each case according to the desired resistivity and strength properties; the material can be for instance cobalt iron, martensitic steel or aluminium-iron alloy.
• the surface plate of the invention when the thickness of the surface plate is larger than the air gap between the rotor and the stator; usually, the thickness must be clearly larger than this.
• the air gaps commonly used in axial flux induction machines are of the order of 1 mm, and thus the thickness of the surface plate is preferably of the order of 1-4 mm, by which the desired result of the invention, that is, essential improvement in efficiency, is achieved.
• the surface plate is essentially level with the surface of the rotor frame, in which case the surface plate closes the ferromagnetic piece out of sight inside the rotor frame.
• the ferromagnetic pieces extend from inside the rotor frame to a distance outside the surface of the frame so that the surface plates at the ends of the ferromagnetic pieces do not touch the rotor frame, but are at a distance from it.
• the surface plate extends outside that surface of the ferromagnetic piece which is against the stator.
• the edges of the surface plates can be placed at a very small distance from each other and in any case notably closer to each other than the ferromagnetic pieces.
• the surface plates are even in contact with each other, that is, they constitute a uniform ring of plates that covers those surfaces of all the ferromagnetic pieces which are against the stator.
• the appropriately ferromagnetic pieces are pieces extending mainly in the direction of the radius of the rotor and essentially taking the form of a truncated narrow sector, that is, the inner ends of the pieces are narrower and the outer ends are wider so that conductor bars of an essentially uniform thickness are formed between these pieces, these bars connecting the outer and inner peripheries of the rotor .
• the ferromagnetic pieces of the rotor are preferably fabricated of common structural steel, for instance Fe52.
• the saturation flux density of this steel grade is high, and the steel grade is therefore suitable for carrying the magnetic flux through the rotor. It is obvious to a person skilled in the art that any material with a high permeability and high saturation flux density may come into question for carrying this magnetic flux through the rotor.
• the material may also be some appropriate composite material with the above-described electromagnetic characteristics. It is preferable for the ferromagnetic parts to have a low electrical conductivity. Usually, however, in steels with a low electrical conductivity, also the saturation flux density is low, and therefore a satisfactory compromise has to be found.
• an electrically highly conductive coating such as copper coating, is arranged on one or both surfaces of the surface plate.
• the electrically highly conductive coating provides as unobstructed, that is, as resistanceless path as possible for eddy currents to minimize losses in the rotor.
• the surface plate structure of the invention can be implemented in axial flux induction machines of different constructions, such as in machines with one stator or two stators. With respect to these different machine constructions, one is referred to the aforementioned patent application WO2006/021616.
• the machine construction of the invention has significant advantages over the known technology. Based on the tests performed, with the machine construction of the invention the efficiency of an axial flux induction machine is improved by 2-4 percentage units, even more than 5 percentage units. This way, it has been possible to decrease the temperature rise of the machine when the power and rotation speed increase.
• Figure 1 shows the cage winding used in a machine of the invention
• Figure 2 is a cut-away drawing showing one embodiment of the invention
• Figure 3 is a cut-away drawing showing a second embodiment of the invention.
• Figure 4 is a cut-away drawing showing a third embodiment of the invention.
• Figure 5 is a cut-away drawing showing a fourth embodiment of the invention.
• Figure 6 shows a detail of the machine of the invention.
• Figure 1 illustrates the rotor construction used in the motor embodiment of the invention, comprising two plates joined together.
• the plates have been machined for instance by precision stamping from work-hardened aluminium alloy sheet.
• the frame plate 8 formed of the cage winding comprises a uniform inner periphery 9 and a uniform outer periphery 10 and conductor bars 11 of the same material, the conductor bars galvanically connecting the peripheries.
• the conductor bars are bars of equal size extending in the direction of the rotor radius, located at even distances between the inner and outer peripheries.
• a plurality of elongated and outwards-widening apertures is thus formed at even distances in the direction of the rotor radius, ferromagnetic pieces 12 of the corresponding shape with the apertures being inserted in the apertures and creating paths for the magnetic flux in axial direction through the otherwise non- ferromagnetic frame plate 8 of the rotor 2.
• Figure 2 illustrates an electrical machine of the invention, in which there is a shaft 1 rotating with respect to the machine frame, and a disc-like rotor 2 supported to the shaft, which is in accordance, for instance, with Figure 1.
• a stator 4 supported to the machine frame and comprising a stator winding 3.
• the ferromagnetic pieces 12 are placed in the apertures extending through the rotor 2 so that together with the rotor plate they constitute a circular plate of a uniform thickness.
• surface plates 5 are attached to the surfaces of the ferromagnetic pieces, these surface plates entirely covering the ferromagnetic pieces 12 and extending somewhat over the rotor frame plate 8.
• the thickness of the surface plates 5 corresponds to or is larger than the air gap 14 between the stator 4 and the rotor 2, the air gap being about 1 mm and the thickness of the surface plate being about l-4mm.
• Figure 3 shows an electrical machine corresponding to Figure 2, with the same reference numerals indicating the same parts as in Figure 2.
• the difference compared with Figure 2 is the ferromagnetic pieces 13, which have been arranged to extend outwards from the surface of the rotor plate 2 towards the stator 4 so that the surface plates 5 are not in contact with the rotor 2 but at an appropriate distance from it. This distance is for instance 3-8 ⁇ un, preferably about 5mm.
• the air gap 14 between the surface plates 5 and the stator 4 is about lmm and the thickness of the surface plate is larger than this, for instance about 2-4mm.
• Figure 4 illustrates an embodiment largely corresponding to that of Figure 3 , in which the ferromagnetic pieces 13 are similar, that is, they extend through the rotor 2 and further to a distance towards the stator 4.
• the surface plate 15 is comprised of a uniform ring, whereas in the embodiment of Figure 3 there is a separate surface plate on each ferromagnetic piece 13, even though the gap between these separate surface plates may be very small.
• a rotor yoke 16 made of ferromagnetic material, such as construction steel, has also been attached to the outer surface of the rotor 2, that is, on the surface opposite the stator 4. This circular plate of a uniform thickness further strengthens the rotor and thus enables even higher rotation speeds.
• the corresponding rotor yoke 16 is only a ring-shaped disc, located only on the ferromagnetic pieces.
• the rotor yoke is not a separate part but it is comprised of the same uniform piece with the ferromagnetic pieces 13.
• a ring-shaped space is formed between the surface plates 5 and 15 and the plate surface of the rotor 2, on the outer periphery of which the ferromagnetic pieces 13 extending out from the rotor constitute radial fins.
• a blower is formed between the rotor and the stator, providing efficient ventilation and removing heat generated in the structures.
• the construction appropriately increases the heat transfer area of the rotor thus improving cooling of the construction .
• Figure 5 shows an embodiment of the invention corresponding to Figure 3, where there is a similar stator construction 4 on both sides of the rotor 2.
• the ferromagnetic pieces 13 extending through the aluminium frame of the rotor 2 project to both sides of the rotor to a distance from the rotor surface.
• Figure 6 is a cut-away drawing showing a detail of a rotor of the invention, where ferromagnetic pieces 18 are extending through the aluminium frame 17.
• the pieces 18 extend to a distance from the surface of the aluminium frame 17, surface plates 19 being attached to the outer surface of these pieces, chese surface plates extending over the edges of the pieces 18.
• nearly closed cavities 20 extending in the direction on the rotor radius are formed on the surface of the rotor, these cavities constituting the efficient fin structure of the centrifugal blower.
• the surface plates 19 form a uniform ring, in which case the cavities 20 are closed at all their sides and open only at their ends .

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Induction Machinery (AREA)
• Iron Core Of Rotating Electric Machines (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=38069478

Family Applications (1)

Country Status (4)

Families Citing this family (6)

Family Cites Families (2)

• 2007
  • 2007-05-03 FI FI20075310A patent/FI20075310A0/fi not_active Application Discontinuation
• 2008
  • 2008-02-28 WO PCT/FI2008/050098 patent/WO2008135628A1/en active Application Filing
  • 2008-02-28 CN CN200880014357A patent/CN101682240A/zh active Pending
  • 2008-02-28 EP EP08718551A patent/EP2143191A1/en not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events