IMPROVEMENTS TO ROTARY GENERATORS

Abstract

An axial flux rotary generator comprising: two magnetic annuli; a coil annulus; the magnetic annuli and coil annulus having a common axis; the two magnetic annuli defining a plurality of magnetic fields around the common axis extending across a gap between the two magnetic annuli and the coil annulus having a sequence of coils around the common axis in the gap such that lines of magnetic flux from the magnetic fields cut the turns of the coils and thus induce electric current in the coils as the magnetic annuli are caused to rotate relative to the coil annulus, means provided at or towards the central aperture of the coil annulus axial to resist flexure of the coil annulus.

Claims

1. An axial flux rotary generator comprising: two magnetic annuli; a coil annulus mechanically braced at an outside periphery; the magnetic annuli and coil annulus having a common axis; the two magnetic annuli defining a plurality of magnetic fields around the common axis extending across a gap between the two magnetic annuli and the coil annulus having a sequence of coils around the common axis in the gap such that lines of magnetic flux from the magnetic fields cut the turns of the coils and thus induce electric current in the coils as the magnetic annuli are caused to rotate relative to the coil annulus; and means provided at the central aperture of the coil annulus to resist axial flexure of the coil annulus.

2. The axial flux rotary generator of claim 1, wherein the aforesaid means to resist axial flexure is in the form of one or more stiffening members, preferably themselves annular, affixed to the central portion of the coil annulus on one or both sides thereof and preferably formed of a material designed to dampen any propensity of the coil annulus to flex axially.

3. The axial flux generator of claim 1, wherein the means to resist axial flexure comprises a bearing.

4. The axial flux generator of claim 3, wherein the bearing is a contact type bearing.

5. The axial flux rotary generator of claim 1, wherein the aforesaid means to resist axial flexure of the coil annulus comprises a plastics bearing surface located upon the coil annulus, acting in sliding contact, or close to sliding contact, with a bearing surface mounted upon the magnetic annuli on either side of the plastics bearing surface located upon the coil annulus.

6. The axial flux rotary generator of claim 5, wherein, when stationary, there is a gap between the bearing surface located on the coil annulus and the bearing surface on the magnetic annuli.

7. The axial flux rotary generator of claim 1, wherein the means further comprises an annular ball race or equivalent.

8. The axial flux rotary generator of claim 7, wherein an inner portion of the annular ball race is affixed to a collar which extends between the magnetic annuli, and an outer portion of the annular ball race is affixed to an inside circular face of the coil annulus.

9. The axial flux rotary generator of claim 1, further comprising an annular collar which extends between the magnetic annuli.

10. The axial flux generator of claim 9, wherein a part of the means to resist axial flexure is mounted on the collar.

11. The axial flux rotary generator of claim 9, wherein, at least a part of the means to resist axial flexure is accommodated within one or more circumferential grooves in the annular collar.

12. The axial flux generator of claim 11, wherein at least a part of the coil annulars extends into the one or more circumferential grooves.

13. The axial flux generator of claim 9, wherein the annular collar is spaced from the common axis.

14. The axial flux rotary generator of claim 1, further comprising channels provided through a collar which extends between the magnetic annuli to enable lubricant to be provided to the means to resist axial flexure.

15. The axial flux rotary generator of claim 1, wherein the coil annulus has a diameter which is at least thirty or more times the axial thickness of the coil annulus.

16. The axial flux generator of claim 1, wherein the means to resist axial flexure is radially inward of all coils of the coil annulars.

Description

[0015] The invention will now be described with reference to the accompanying drawings in which:

[0016] FIG. 1a shows an exploded view of a generator of the type to which the present invention may be applied and FIG. 1b shows a stator and rotors to scale;

[0017] FIG. 2 shows a first form of arrangement to limit stator axial flexure;

[0018] FIG. 3 shows a second form of arrangement for limiting axial flexure;

[0019] FIG. 4 shows a third form of arrangement for limiting axial flexure;

[0020] FIG. 5a shows a coil annulus populated with coils;

[0021] and

[0022] FIG. 5b shows means for lubricating the means of FIGS. 2 to 4 during use.

[0023] Referring to FIG. 1a, annular magnet bearing rotors of an axial flux generator are shown at 10, 11 and 12. The magnets 6, 7, 8 & 9 mounted around the peripheries of rotors to form magnetic annuli face each other across an air gap. Annular collars 13 and 14 extending between and separating the rotors 10-12 at their inner portions and maintain a precise spacing between them. The annular collar is spaced from the common axis. The rotors 10-12 and collars 13, 14 are bound together by draw bolts, 15 and 16. Coil carrying stators 17 and 18 form coil annuli and are sandwiched between the three rotors 10-12.

[0024] The magnetic annuli and coil annuli have a common axis. Two magnetic annuli define a plurality of magnetic fields around the common axis extending across the gap between the two magnetic annuli. The sequence of coils of the coil annuli around the common axis in the gap are such that lines of magnetic flux from the magnetic fields cut the turns of the coils and thus induce electric current in the coils as the magnetic annuli are caused to rotate relative to the coil annulus.

[0025] For certain applications, very large diameter generators may be utilised having diameters of five six or even seven meters. These are needed where the rate of rotation of the rotors is particularly slow, for example as when directly driven by the rotor of a wind turbine. Examples could be as low as 16 or 14 rpm. The peripheral speed of the rotors acquired through their sheer diameter, and thus the increased rate at which lines of flux from their magnets cuts the coils sandwiched between them, compensates for the absence of a gearbox to speed up the rate of rotation to the normal ranges of rpm associated with small diameter rotary generators, for example 1500 rpm.

[0026] An example is shown to scale at FIG. 1b of such a large diameter arrangement. A large diameter annular stator is in effect simply a thin plate having a central aperture. Two rotors 19 and 20, sandwich a stator 21. In current designs there is no form of axial support for the stator towards its centre portion, 22. Mechanical bracing is available at the outside periphery of the stator, as shown at 23, to keep the stator aligned correctly between its rotor plates, but its effectiveness reduces towards the central area. The majority of the stator's area is inaccessible, being as it is closely sandwiched between the substantially equal diameter rotors on either side of it. Typically, a stator may be of diameter seven meters, but only 50 mm in axial thickness. This renders it in effect flimsy in an axial sense towards its centre, and vulnerable to axial perturbations. The physics of the forces arising during generation dictate that the torque experienced by the coils should lie entirely in a planar sense and therefore within the plane of the stator and so developers have assumed that very axially thin coil annuli, which are preferred in terms of having a small gap between magnetic annuli and so increase generation efficiency and to keep costs low are sufficient. However, the present inventor has surprisingly found experimentally that parasitic forces may arise resulting also in axial flexure of the stator, as shown by the arrow. In the real world there is a real risk that any vibrations arising in the axial sense during operation of the generator, as might be caused by asymmetrical cyclic forces experienced by the stator coils as emfs are generated within them, could result in the surfaces of the stators scraping against the rotor mounted magnets on either side of them. Heavy and possibly catastrophic damage can result.

[0027] A first method of addressing this is shown with reference to FIG. 2. This shows in expanded detail the upper half central area of the generator of FIG. 1. The stator 24 of the coil annulus is shown in this case fitted with a means to resist axial flexure in the form of annular stiffening members 25 and 26 constructed from materials and to dimensions designed to limit any tendency to axial flexure. The annular stiffening members effectively increase the axial thickness of the coil annulus at a radially inner portion. The annular stiffening members may be integral or non-integral with the plate forming the stator in which the coils are embedded. The radial lengths of magnets 27 and 28 mounted around the rotors 29 and 30 of the magnetic annuli are limited in length to provide a recess 30a to accommodate the annular stiffening members 25, 26. The means to resist axial flexure are radially inward of all coils thereby to give over as much space as possible to the electricity generating components and to achieve best mechanical advantage.

[0028] A second method is shown with reference to FIG. 3. In this case, rather than the annular stiffening members of FIG. 2, the means to resist axial flexure is a bearing, for example a contact bearing. In the example of FIG. 2 the inner portions of the stator plate are equipped with bearing proprietary plastics surfaces, 31 and 32. The rotors are similarly equipped as shown at 33 and 34. In the event of any tendency of the stator to move in the axial sense, the bearing plates are present to prevent this. To avoid excessive wear, the plates need not be in permanent contact, thus a small airgap is present between them as shown.

[0029] A third method is shown with reference to FIG. 4. For especially heavy duty applications, for example generators generating at the rate of 1 MW or more, and where parasitic axial forces may be greater/more apparent, it may be desirable to utilise a more heavy duty solution to overcome entirely any propensity for stator axial vibrations or movement.

[0030] In this case, a formal annular ball race or equivalent may be utilised, as shown at 35. A part of the means to resist axial flexure, for instance the inner portion of the ball race, is affixed to the central collar 36, and the outer portion to the inside circular face 37 of the stator 38. In this case, and given the precision with which such bearings are now manufactured and assembled, virtually no movement in the axial sense is possible.

[0031] It is important for any generator of this form of construction for as much stator area as possible to be utilised and populated with coils, an example being shown at FIG. 5a. The greater the number of turns, the greater the output.

[0032] A method of ensuring that any of the foregoing arrangements do not impinge on this generating area is shown at FIG. 5b. Rather than the surface arrangements shown at FIGS. 2 to 4, a groove may be provided in the central collar as shown in FIG. 5b at 39. The stator 40 can dip into or project into this groove, with any of the aforegoing disclosed movement constraining methods being confined to this area. In the case shown at FIG. 5b, bearing plastics are shown within the groove at 41, 42, and upon the stator at 43 and 44. As can be seen in comparison with FIG. 4, this enables both the magnets 27 and 28 to be longer in radial length and similarly the stator coil 45, thereby facilitating an increase in the emfs generated.

[0033] As part of the routine maintenance of a generator equipped with the means of the present invention, it may be desirable to provide lubrication periodically. Lubrication grooves or channels 46 are to this end located through the collar, reaching into the groove 39 to allow for suitable lubricants to reach the operative surfaces from the inside of the annular collars 13, 14.

[0034] Numerous variations will be apparent to those skilled in the art.