ROTOR CONSTRUCTION FOR WINDMILL

Abstract: Device for converting wind flow energy into mechanical energy, having a base construction (4) and a rotor (8) having a number of rotor blades (20; 20a) which are connected to an annular rotary support (18) and extend essentially in a plane through the axis of rotation (14) of the support. The wind-braking area of the rotor (8) is adjustable. Each rotor blade (20; 20a) or a part thereof is hingedly connected to the rotor support (18) for setting the rotor blade or part thereof in a predetermined lengthwise orientation at a predetermined distance relative to the axis of rotation (14) of the support by moving the rotor blade or part thereof in a plane through the axis of rotation. The rotor blades (20; 20a) may be directly hingeably connected to the rotor support (18), or by means of an arm assembly (17; 22; 24). The rotor blades are made up of a number of elongated parts (74, 76, 78; 92) for varying the effective length of the blades.

Description: Rotor construction for windmill. The invention relates to a device for converting wind flow energy into mechanical energy, comprising a base construction and a rotor mounted on the base construction, the rotor having a number of rotor blades which are connected to a rotary support and extend essentially in a plane through the axis of rotation of the support, the wind-braking area of the rotor being adjustable. Such a device is known from EP-A-0 016 602, which describes a windmill having a rotor with a central hub which is connected to an annular augmenter by a plurality of radial cables, which support a plurality of radial rotor blades. In a particular embodiment, the rotor blades each are made up of a number of templates covered by a flexible membrane. The length of a blade can be adjusted by moving the templates, and thereby the membrane, along the cables. Accordingly, the wind-braking area is varied. By this measure, the effective rotor diameter of the windmill can be increased at relatively low wind speeds, with the result that the power generated by the windmill can also be high in this wind speed range, at any rate higher than in the case of a windmill with vanes of a fixed length. At relatively high wind speeds the effective rotor diameter of the windmill can be reduced, with the result that the windmill can be kept in operation in this wind speed range with maximum power output, without the risk of damage to the rotor blades. A disadvantage of the known device is its great number of component parts which makes the device complex to build, to service and to repair. Moreover, each cable gives rise to turbulence, which lowers the efficiency of the device. Another disadvantage of the known device is that the rotor blade shape cannot be maintained at strong winds, the membranes deforming between the templates. The object of the invention is to provide a device in which the wind-braking area of the rotor and the effective length of the rotor blades is adjustable, and which has a simpler construction compared to the prior art devices, with relatively few component parts. To reach this aim, the device according to the invention is characterised in that each rotor blade or a part thereof is hingedly connected to the rotor support for setting the rotor blade or part thereof in a predetermined lengthwise orientation at a predetermined distance relative to the axis of rotation of the support by moving the rotor blade or part thereof in the plane through said axis of rotation. By pivoting the rotor blades or parts thereof from a position in which they are essentially at right angles to the wind direction to an orientation in which they are at a small angle or parallel to the wind direction, the wind-braking area of the rotor can be effectively" adjusted to the actual wind speed. On the other hand, the wind-braking area can be adjusted by keeping the rotor blades or parts thereof at right angles to the wind direction, and using the hinged connections to the rotor support according to the invention to move the rotor blades or parts thereof to and from the axis of rotation of the rotor support to adjust the effective length of the rotor blades. Preferably, the hinge axis for a rotor blade is directed essentially at right angles to the plane through the axis of rotation of the support, in which plane the rotor blade extends. This is one of the simplest ways of connecting a rotor blade to the support of the rotor, not affecting the angular position of the rotor blade with respect to its longitudinal axis and with respect to the plane through the axis of ratation of the support when changing the setting of the rotor blade. However, if it is desired to change said angular position of the rotor blade simultaneously with changing the setting of the rotor blade, the rotor blade advantageously is connected to the support in such a way that a hinge axis for a rotor blade is directed at an acute angle both to the plane through the axis of rotation of the support, in which plane the rotor blade extends, and to the axis of rotation itself. In a preferred embodiment, the part of the rotor blade facing the axis of rotation of the support of the rotor is hingedly connected to the support. The maximum wind-braking area, to be used at relatively low wind speeds, is achieved when the rotor blades are at right angles to the wind direction, while pivoting the rotor blades away in the wind direction and/or pivoting the rotor blades around their longitudinal axes results in a lower wind-braking area to be used a relatively high wind speeds. Since the part of a windmill rotor blade which is facing away from the axis of rotation of the rotor is most effective for generating power, in another preferred embodiment the support of the rotor is hingedly connected to each rotor blade through an arm assembly, the part of the rotor blade facing the support being situated at a distance from the support. In this way the comparatively little effective part of each rotor blade has been replaced by the arm assembly. Although in principle one arm for each rotor blade suffices, particular rotor blade pivoting movements can be easily achieved if the arm assembly comprises at least two arms for each rotor blade, the arms being situated radially next to each other, one end of each arm being coupled to the rotor blade and the other end of each arm being coupled to the support. When the coupling points of the arms to the rotor blade are situated at a first distance from each other, and the coupling points of the arms to the support are situated at a second distance from each other which is smaller than the first distance, pivoting of the arms over a certain angle results in the associated rotor blade pivoting over a smaller angle. When the second distance is equal to the first distance, pivoting of the arm over a certain angle does not result in any pivoting of the associated rotor blade. Preferably, the support of the rotor blades is annu¬ lar, and is mounted in such a way on the base construction that it is supported to allow rotation about its own centre point. Such a support, which a properly chosen inner and outer diameter, provides enough area along its. length for the hinged connections to be made. The support may e.g. be made in the form of an annular tube. The energy conversion by the device according to the invention can be made more constant and less dependent from wind speed variations by giving the rotor the properties of a flywheel. For this purpose, the mass of the annular support of the rotor blades is made high relative to the mass of the rotor blades. If the support has the form of an annular tube, this tube may e.g. be filled with sand or another filler material to increase its mass. In a preferred embodiment the annular support is mounted at its radial outer side in a number of rotatable bearing elements. The bearing elements may be small in diameter and consist of conventional roller bearings, but may also have larger diameters. When the rotor has a sufficiently large mass, it will be possible to provide the bearing elements only at the lower part of the support. Advantageously, at its radial outer side the support is detachably coupled to the drive wheel of a generator. A friction coupling may generally be satisfactory. When using a plurality of generators each coupled to a bearing element, the annular support of the rotor blades can be used for energy generation distributed along a part of, or the whole circumference of the support. By coupling or decoupling drive wheels of generators, the energy generation can be adapted to the actual demand. Also maintenance and repair can be done without interrupting the operation of the device. When the support has a number of spokes joining at the axis of rotation of the support in a bearing element, the spokes being directed at an acute angle to the axis of rotation of the support, a simple and light-weight bearing construction is obtained. Another stiff construction which also has good wind-guiding properties is obtained when the support is the base of an essentially cone-shaped reinforcement element, the top of the reinforcement element being on the axis of rotation of the support and being mounted in a bearing element. In order to further increase the versatility of the device according to the invention, and in particular to increase the adjustability of the wind-breaking area to the actual wind speed, the rotor blades are formed by a number of elongated rotor blade parts, which are adapted to be placed in a position fully or partially overlapping each other in the lengthwise direction, or essentially in line with each other. For a minimum length of such a rotor blade, the component parts of the rotor blade fully overlap each other. A maximum length of such a rotor blade is achieved if all component rotor blade parts are placed in line with each other. A first advantageous possibility is that a first rotor blade part is connected to a second rotor blade part in such a way that it can slide essentially parallel to the second rotor blade part in the lengthwise direction there- of, and provision is made for drive means for sliding the first rotor blade part over a predetermined distance relative to the second rotor blade part. A minimum length of the rotor blade is achieved if the rotor blade parts fully overlap each other, and the maximum rotor blade length is achieved if the rotor blade parts are placed in line with each other. Any intermediate length of the rotor blade can be set by selecting a suitable overlap of the rotor blade parts, so that a continuous rotor blade length adjustment is possible. A second rotor blade part preferably comprises an internal space in which the first rotor blade part can be accommodated. A flexible, light-weight embodiment of drive means for rotor blade parts is obtained by using flexible wire- type elements, for example, Bowden cables or wires which can absorb both pressure and tensile forces. In another preferred embodiment, the rotor blades comprise one or more flexible casings to which a fluid can be supplied, for the purpose of filling the casings, so that they assume the shape of a rotor blade or rotor blade part, and from which casings the fluid can be discharged, for the purpose of emptying the casings, so that they lose the shape of a rotor blade or rotor blade part. A particularly light-weight construction can be obtained if a gas, for example air, is selected as the fluid. However, it is also possible to use a liquid for filling the casings. In the last-mentioned embodiment, each rotor blade preferably consists of a number of casings which are placed one after the other in the lengthwise direction thereof, and by means of which the length of the rotor blade can be simply increased or reduced in stages to the desired size. In order to improve the rigidity of a rotor blade which is made up of fluid-filled casings, the casings of the rotor blades can be supported by a frame which determines the setting and position of the casings in the filled and empty state. Such a frame can in turn be filled with a fluid at a predetermined pressure, in order to increase the rigidity of the frame. A particularly advantageous embodiment is obtained if the frame comprises a system of channels with controllable valves, by means of which a connection can be produced selectively between a casing and a fluid supply line or fluid discharge line. The frame can be constructed of e.g. hollow tubes, which themselves form the above- mentioned channels. The invention is explained with reference to the drawings, in which: Fig. 1 shows a diagrammatic side view of a first embodiment of a device according to the invention in an off-shore application; Figs. 2 - 4 show diagrammatic side views of other embodiments of the device according to the invention in land applications; Fig. 5 shows on a larger scale a detail V of the device of Fig. 1; Fig. 6 shows, partially in cross-section, a detail VI of the device of Fig. 1; Fig. 7 shows an alternative construction for the part of the device shown in Fig. 6; Fig. 8 shows on a larger scale a back view of a part of an annular rotor support hingedly connected to an arm assembly which is provided with a rotor blade similar to the device of Fig. 1; Fig. 9 shows a side view of the rotor part of Fig. 8; Fig. 10 shows on a larger scale a rotor construction for the device of Fig. 2 in a view similar to Fig. 9; Fig. 11 shows on a larger scale a top view of a part of the rotor in the direction of arrow XI in Fig. 10; Fig. 12 shows a perspective diagrammatic view of another rotor embodiment according to the invention; Fig. 13 shows a diagrammatic, partially cut-away view in perspective of another embodiment of a rotor blade; and Fig. 14 shows a diagrammatic view of a rotor blade in another embodiment similar to the device of Fig. 4. In the figures similar reference symbols indicate similar parts. Fig. 1 shows a windmill with a base construction 4 in the form of a tower fixed on a platform 1 floating in water 3. The top part of the tower accommodates the bearings for a rotor 8 and means for converting wind flow energy into a suitable other form of energy. The top part of the tower can be rotated (shown symbolically by means of a double arrow 10) about a vertical axis 4a by means of a turning device (not shown in any further detail) in such a way that the rotor 8 can be directed as fully as possible into the wind having a direction according to arrow 12. The rotor 8, the axis of rotation of which is indicated by a dashed line 14, comprises a plurality of spokes 16 directed at an acute angle to the axis of rotation 14, on the ends of which spokes a ring 18 is fixed. The ring 18 is mounted on bearings which are shown in further detail in Fig. 6, whereas the spokes 16 join at another bearing element which is shown in further detail in Fig. 5. The ring 18 bears a number of arms 17 which, at the end thereof facing away from the ring 18, are provided with rotor blades 20, the length of which can be varied, for example in one of the ways indicated below on the basis of Figs. 12 and 13. The arms 17 are hingedly connected to the ring 18, so that the position and orientation of the rotor blades 20 relative to the axis of rotation 14 can be varied between a position A and a position B, the latter being indicated with dashed lines. A wind-braking area can thus be obtained, with a radius varying between radius Rl and radius R2, depending on the wind speed. The platform 1 is anchored by a line 19a to a buoy 19 fixed to a bottom 21, which line 19a is also used to transfer the energy generated by the windmill to the buoy 19. From the buoy 19 the energy is transported further by means of a line 19b, possibly after a conversion into a more suitable form, to an area where it is used. Figs. 2 and 3 show devices which are similar to the one depicted in Fig. 1, each being anchored in a ground 2. Here the ring 18 is fixed to a cone-shaped reinforcement element 16a. In these embodiments the rotor blades 20 are hingedly connected to the ring 18 by arm assemblies 22 and 24, respectively, each consisting of two arms which are situated radially next to each other. One end of each arm is hingedly connected to the rotor blade 20 and the other end of each arm is hingedly connected to the ring 18. In Fig. 2 the coupling points of the arms 22 to the rotor blade 20 are situated at a first distance from each other, and the coupling points of the arms 22 to the ring 18 are situated at a second distance from each other which is smaller than the first distance. As a result, when pivoting the arms 22 from the position C to the position indicated with D, the rotor blades 20 will pivot to a lesser extent. In Fig. 3, the first distance between the coupling points of the arms 24 to the rotor blade 20 is equal to the second distance between the coupling points of the arms 24 to the ring 18. As a result, when pivoting the arms 24 from a position E to a position F, the orientation of the rotor blades 20 connected to the arms 24 will remain the same, while the rotor blades 20 move closer to the axis of rotation 14. In the embodiment shown in Fig. 4 the rotor blades 20 are directly hingedly connected to the ring 18. At high wind speeds, the rotor blades can be pivoted from a position G to a position H to be able to keep the windmill in operation and at the same time reducing the stresses on the rotor blades 20, the rotor bearings and the base construction 4. Referring to Fig. 5, at the point where the spokes 16 supporting the ring 18 come together, a flange connection 25 to a shaft 27 is made. The shaft is accomodated in a combined roller and thrust bearing 26. For repair and maintenance, the flange connection 25 may rest in a U-shaped support 28. The bearing 26 is fixed on the top part of the base construction 4. In Fig. 6 and 7 a tubular ring 18 with a circular cross-section is shown. For clarity, neither rotor blades nor arms for supporting rotor blades and fixed to the ring 18, are shown. Spokes 16 support the ring 18 to keep it into shape. The hollow ring 18 may be filled with solid material, e.g. sand, to increase its inertia. Referring to Fig. 6, the ring 18 is mounted on roller bearings 29, of which the curve of the outer surface is complementary to the curvature of the outer surface of the ring 18. The roller bearings 29 are fixed on the top part of the base construction 4 of the windmill and may be placed at regular intervals along the circumference of the ring 18. In Fig. 7 the ring 18 is coupled to one or more relatively large rollers 30, which are drive wheels for directly mechanically coupled generators 32, e.g. for converting the mechanical energy delivered by the ring 18 to the roller 30 into electrical energy. The rollers 30 may be made of flexible material, such as a rubber compound, and be in friction engagement with the ring 18. The rollers 30 and the generators 32 are provided movably on the top part of the base construction 4 (symbolically indicated by double arrow 31) such that the rollers 30 may be brought into, or out of contact with the ring 18 to be able to tune the energy generation to the actual energy demand. Rollers 30 and generators 32 may be placed at regular intervals along the circumference of the ring 18. Figs. 8 and 9 illustrate a rotor blade adjusting device for the windmill shown in Fig. 1. For simplicity, only one rotor blade 20 and the associated adjusting device are shown. The arm 17 can be pivoted around a shaft 34 fixed to the ring 18. In this way, the orientation of the arm 17 and the associated rotor blade 20 can be varied between the position A and the position B. For setting such positions, the base of the arm 17 at a point 36 is hingedly connected to the end of a piston rod 38 of a cylinder- piston unit 40, which in turn is hingedly connected to one of the spokes 16. The rotor blade 20 can be pivoted around a longitudinal axis by means not shown for setting the angle of the rotor blade 20 with respect to the wind direction 12. In addition to this, a resilient element may be built in the connection between the arm 17 and the rotor blade 20, so that the rotor blade may yield when sudden gusts of wind occur. Fig. 10 shows in more detail the rotor construction according to Fig. 2. At points 42 and 44 arms 22 are hingedly connected to the ring 18, whereas at points 46 and 48 the arms 22 are hingedly connected to the rotor blade 20. At the hinge point 42, one of the arms 22 is fixed to a gear wheel 50. The gear wheel 50 is in engagement with a second gear wheel 52, which can be driven by means not shown in any further detail. By driving the gear wheel 52, the arms 22 can be moved in the area between the position C and the position D for setting the wind-braking area of the rotor. By Fig. 11 the form of an embodiment of a rotor blade is illustrated, as well as the way in which such a rotor blade 20 can be brought out of the wind (indicated in dashed lines) blowing in the direction of arrow 12. The rotor shown in Fig. 12 has a support which essentially consists of a ring 18 and a cone-shaped reinforcement element 54. At the inside of the reinforcement elements 54 a number of drive elements 56 is fixed, only one of which is shown in the figure. The drive element 56 has a rotatable shaft 57 defining a hinge axis for a rotor blade 20a. The shaft 57 is directed at an acute angle both to the plane through the axis of rotation 14 of the support, in which plane the rotor blade 20a extends, and to the axis of rotation 14 itself. The rotor blade 20a is fixed to the shaft 57 at an angle which is larger than 90°. By rotating the shaft 57, the rotor blade 20a can be brought from the position K to the position L shown in dashed lines. As a result of the particular orientation of the hinge axis, the rotor blade 20a, while pivoting from position K to position L, at the same time pivots around its longitudinal axis. Both pivoting movements bring the rotor blade 20a out of the wind blowing in the direction 12. Fig. 13 shows a part of a ring 18 of the rotor 8. An elongated, hollow first rotor blade part 74 is hingedly connected to the arm 17, which first rotor blade part 74 can contain an elongated, hollow second rotor blade part 76. The second rotor blade part 76 can in turn contain an elongated third rotor blade part 78. The rotor blade parts can be shifted relative to each other in the lengthwise direction thereof by means of drive means fitted in the first rotor blade part 74, comprising a motor 80 which can drive a spindle 82. Wound on the spindle 82 is a wire 84 which can be subjected to both tensile stress and pressure, and which is led in a suitable manner into the interior of the first and second rotor blade part 74 and 76, for the purpose of shifting the third rotor blade part 78. Drive means for the second rotor blade part 76 can be provided in a similar way. Fig. 14 shows a rotor ring 18 with a rotor blade 20a hingedly connected thereto. The rotor blade 20a made up of a frame 90 with four frame parts which can be closed selectively by filling a flexible casing 92 with a fluid for setting the effective wind-catching area of the rotor. In the case of rotor blade 20a two of the four frame parts are thus closed, while the two frame parts at the free end of the rotor blade are open, and the corresponding casing 92 is empty and extends along the frame 90. The frame 90 comprises a system of channels with controllable valves 96 and 97, by means of which a connection can be produced selectively between a casing 92 and a fluid supply line 98 or fluid discharge line 99. The control of the rotor blade position, orientation and length can be achieved by measuring the current wind speed at a distance from the windmill and, on the basis of the result of this measurement, setting such a wind-braking area the mechanical power generated by the windmill is held approximately constant, taking into account the limits of the mechanical stress which the windmill parts can bear. Another control criterion can be the maximisation of the mechanical power generated in the prevailing wind. Although various embodiments for setting the rotor blades are described in the above, it will be clear that any desired combination of the described embodiments can also be used.

Claims: Claims 1. Device for converting wind flow energy into mechanical energy, comprising a base construction (4) and a rotor (8) mounted on the base construction, the rotor (8) having a number of rotor blades (20; 20a) which are connected to a rotary support (18) and extend essentially in a plane through the axis of rotation (14) of the support, the wind-braking area of the rotor (8) being adjustable, characterised in that each rotor blade (20; 20a) or a part thereof is hingedly connected to the rotor support (18) for setting the rotor blade or part thereof in a predetermined lengthwise orientation at a predetermined distance relative to the axis of rotation (14) of the support by moving the rotor blade or part thereof in the plane through said axis of rotation. 2. Device according to claim 1, characterised in that a hinge axis for a rotor blade (20) is directed essentially at right angles to the plane through the axis of rotation (14) of the support (18) , in which plane the rotor blade extends. 3. Device according to claim 1, characterised in that a hinge axis for a rotor blade (20a) is directed at an acute angle both to the plane through the axis of rotation (14) of the support (54, 18), in which plane the rotor blade extends, and to the axis of rotation itself. 4. Device according to claim 1, 2 or 3, characterised in that the part of the rotor blade (20) facing the axis of rotation (14) of the support (18) of the rotor (8) is hingedly connected to the support. 5. Device according to claim 1, 2 or 3, characterised in that the support (18) of the rotor (8) is hingably connected to each rotor blade (20) through an arm assembly (17; 22; 24), the part of the rotor blade facing the support being situated at a distance from the support. 6. Device according to claim 5, characterised in that the arm assembly comprises at least two arms (22; 24) for each rotor blade (20) , the arms being situated radially next to each other, one end of each arm being coupled to the rotor blade and the other end of each arm being coupled to the support (18) . 7. Device according to claim 6, characterised in that the coupling points of the arms (22; 24) to the rotor blade (20) are situated at a first distance from each other, and the coupling points of the arms to the support (18) are situated at a second distance from each other,which is smaller than or equal to the first distance. 8. Device according to any of claims 1-7, characterised in that the support (18) of the rotor blades (20) is annular, and is mounted in such a way on the base construction (4) that it is supported to allow rotation about its own centre point. 9. Device according to claim 8, characterised in that the mass of the support (18) of the rotor blades (20) is high relative to the mass of the rotor blades. 10. Device according to claim 8 or 9, characterised in that the support (18) is mounted at its radial outer side in a number of rotatable bearing elements (29) . 11. Device according to any of claims 8-10, characterised in that at its radial outer side the support (18) is detachably coupled to the drive wheel (30) of a generator (32) . 12. Device according to any of claims 8-11, characterised in that the support (18) has a number of spokes (16) joining at the axis of rotation (14) of the. support in a bearing element (26) , the spokes being directed at an acute angle to the axis of rotation of the support. 13. Device according to any of claims 8-11, characterised in that the support (18) is the base of an essentially cone-shaped reinforcement element (54) , the top of the reinforcement element being on the axis of rotation (14) of the support and being mounted in a bearing element. 14. Device according to any of claims 1 - 13, characterised in that the rotor blades are formed by a number of elongated rotor blade parts (74, 76, 78; 92), which are adapted to be placed in a position fully or partially overlapping each other in the lengthwise direction, or essentially in line with each other. 15. Device according to claim 14, characterised in that a first rotor blade part (76, 78) is connected to a second rotor blade part (74, 76) in such a way that it can slide essentially parallel to the second rotor blade part in the lengthwise direction thereof, and provision is made for drive means (80) for sliding the first rotor blade, part over a predetermined distance relative to the second rotor blade part. 16. Device according to claim 15, characterised in that the second rotor blade part (74, 76) comprises an internal space in which the first rotor blade part (76, 78) can be accommodated. 17. Device according to any of claims 14 - 16, characterised in that the rotor blade parts (74, 76, 78) can be moved relative to each other by using flexible wire- type elements (84) . 18. Device according to claim 17, characterised in that the wire-type elements (84) consist of Bowden cables. 19. Device according to any of claims 1 - 14, characterised in that the rotor blades comprise one or more flexible casings (92) to which a fluid can be supplied, for the purpose of filling the casings, so that they assume the shape of a rotor blade or rotor blade part, and from which casings the fluid can be discharged, for the purpose of emptying the casings, so that they lose the shape of a rotor blade or rotor blade part, and in that means (96, 97, 98, 99) are provided for selectively supplying fluid to and discharging it from the casings. 20. Device according to claim 19, characterised in that each rotor blade consists of a number of casings (92) placed one after the other in the lengthwise direction thereof . 21. Device according to claim 19 or 20, characterised in that the casings (92) of the rotor blades are supported by a frame (90) which determines the setting and position of the casings in the filled and empty state. 22. Device according to claim 21, characterised in that the frame comprises a system of channels with controllable valves (96, 97) , by means of which a connection can be produced selectively between a casing (92) and a fluid supply or fluid discharge line (98, 99) .

Inventors: EIKELENBOOM PIETER ARIE JAN, EIKELENBOOM, PIETER, ARIE, JAN
Applicants: EIKELENBOOM PIETER ARIE JAN, EIKELENBOOM, PIETER, ARIE, JAN
Application year: 1993
Main classification: F03D7
IPC codes: F03D1, F03D7, F03D11