Wind turbine

Abstract: A wind turbine of the type having a rotor with a relatively large number of blades. According to the invention the blades are mounted one behind the other on a central shaft (30) of the rotor; at least a number of blades are mounted for free rotation relative to the central shaft of the rotor; the freely rotatable blades are coupled to adjacent blades by catch means (55); detecting means are provided for detecting impending overload of the rotor, and blade adjusting means (61-66) ar provided which in response to such impending overload can turn the blades mounted for free rotation relative to the central shaft and at least one blade (35,36) fixedly connected to said shaft relatively to one another so that said blades become at least partially aligned one behind the other.

Description: This invention relates to a wind turbine of the type having a rotor with a relatively large number of blades. Such wind turbines, which are known by the name of American wind turbine or polder draining mill, are known per se, for instance from "Wind en Energie", Felix von König, Kluwer Technische Boeken, Deventer, 1980, and are used for various purposes, such as pumping water of generating electricity, and the like. A great advantage of this type of wind turbine is that useful energy is already provided at a low wind force. Another advantage is that such a wind turbine operates with a low speed of the wheel or rotor, so that, under normal conditions, the mechanical load is relatively low, and the blades may be simple and hence inexpensive. A disadvantage of the American wind turbine is that, owing to the large number of vanes, it has a large wind catching area, and consequently has a poor resistance to high winds, let alone to gale. Indeed, the known multi-blade wind turbines should be provided with a transverse wind vane, which at a pre-determined wind force automatically turns the rotor out of the wind. In this way, the wind turbine can be prevented from being damaged at high winds, it is true, but at the same time it will cease to provide energy. It is an object of the present invention to overcome the disadvantage outlined above. For this purpose, according to the present invention, a wind turbine of the kind described is characterized in that the vanes are mounted axially behind each other on a central shaft of the rotor; that at least a number of vanes are mounted for free rotation around the central shaft of the rotor while at least one vane is fixedly connected to the central shaft; that the freely rotatable vanes are coupled to adjacent vanes by catch means; and that detection means are provided for detecting impending overload of the rotor, and vane adjusting means which in response to such impending overload can rotate said freely rotatable vanes relatively to the central shaft so that said vanes at least partially become axially aligned. It is noted that FR-A-1013456 discloses a wind turbine having a number of vanes which in order to avoid overload van pivot relative to the central shaft of the wind turbine around an axis perpendicular to the axis of the central shaft. Thus the vanes can fold together in the manner of the petals of a flower. A similar wind turbine has been disclosed in DE-A-647287. The vanes of said known wind turbines however are all basically mounted in one and the same plane perpendicular to the axis of the centrale shaft and cannot rotate around said shaft in the manner of a fan like the vanes of the inventive wind turbine. One embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Fig. 1 is a front-elevational view, showing a part of a wind turbine with a relatively large number of blades; Fig. 2 illustrates the principle of the present invention; Fig. 3 shows a side-elevational view of a part of an embodiment of a wind turbine according to the present invention; Fig. 4 shows a detail of an embodiment of a wind turbine according to the present invention; Fig. 5 shows a cross-sectional view of an example of a special adjustable blade for use in a wind turbine according to this invention; and Fig. 6 shows the way in which such adjustable vanes can be adjusted. Fig. 1 shows diagrammatically and in front-elevational view, an example of a rotor 1 of a wind turbine having a relatively large number of vanes. In the example shown, the rotor has a central shaft 2 and twelve blades 3-14, mounted pairwise on a common rod 15-20. Such a wind turbine is sometimes called an American wind turbine, and in practice may have a different, often larger, number of vanes. Fig. 2 illustrates the principle of the present invention. Fig. 2 shows a rotor similar to Fig. 1, but now vanes 3, 4 and the associated vanes 9, 10 are visible only. The other vanes have been turned behind the vane pair 4, 10 by means of a catch 21. For clarity, Fig. 2 shows the other vanes in their original position in ghost outline, and catch 21 is also shown in its inoperative position at 21′. At normal wind force, the rotor has the shape shown in Fig. 1. At high wind, the vanes are increasingly shifted one behind the other by means of the catch or other suitable mechanism. First, vane 8 (and the associated vane 14) are turned behind vane 7 (and vane 13). When the wind force is increasing further, the packet of vanes 8 and 7 (with the associated vanes 14 and 13) are turned behind vane 6 (and vane 12), etc. At very high wind, all pairs of vanes have been turned one behind the other to form a vane packet which behaves as a single pair of vanes. In the example shown, all pairs of vanes have then been turned behind vanes 3 and 9. Thus, when the wind force is increasing, the wind catching area of the rotor gradually decreases, so that damage to the wind turbine is prevented. Fig. 3 shows diagrammatically and in side-elevation view a part of en embodiment of a wind turbine according to the present invention. For clarity, in the example shown, only the central sections of three pairs of vanes are shown. Fig. 3 shows a central shaft 30 of rotor 31 of a wind turbine. Mounted on the central shaft are three pairs of vanes. Each pair of vanes has a common rod 32,33,34, and in this example, each rod carries two vanes 35,36; 37,38; and 39,40, respectively, spaced from the central shaft. The pairs of vanes are not, as conventional, all situated in the same plane, but are mounted on the central shaft one behind the other. Vanes 35,36 form the front pair of vanes. Behind the vanes, the central shaft is journalled in bearings 41,42, shown diagrammatically, mounted on parts 43 of a substructure of the wind turbine. There is further diagrammatically shown a pulley 44, by means of which an apparatus to be driven, such as a pump, a generator, or the like, can be coupled to the central shaft. However, the drive can alternatively be effected by other known per se means, for example, by means of pulleys as shown, sprocket wheels, gear wheels, a universal joint, etc. Rod 32 is fixed to the central shaft 30, as shown diagrammatically at 45. Rods 33 and 34, however, are rotatable relative to the central shaft, and may be mounted on the central shaft through the intermediary of a bearing bushing 46,47, or even a ball bearing. In principle, therefore, rods 33 and 34 are freely rotatable relative to the central shaft. However, the vanes, or the rods of the successive pairs of vanes are coupled together through catch means. These catch means permit an angular rotation α between two successive vanes, ranging between 0 degrees and a pre-determined maximum angle of αmax. Generally speaking, angle αmax is 360 degrees/n, where n is the number of vanes, but this is not strictly necessary. In the example of Fig.2, angle αmax is 30 degrees. At high winds, α = 0 degrees, and the vanes are located right one behind the other. At normal wind, α = αmax , and the vanes are maximally spread out. The catch means may consist of chains, ropes, or rods, strips or bars hinged together and to the respective vanes, mounted in each case between two successive vanes or rods. Fig. 4 shows diagrammatically an embodiment in which each one vane 50 is provided with a catch which engages in a groove 52 in the other vane 53, which groove is closed at least at the end pointing in the direction of rotation. The direction of rotation is indicated by an arrow P. In this example, the leading vane 50 is provided with a catch, and the trailing vane has a groove. Alternatively, vane 50 could have the groove and vane 53 the catch. Furthermore, the catch could be secured to a lateral projection of a vane, if a larger angle between two successive vanes is desirable, or the connection should be located further from the central shaft. In Fig. 3, catches are shown diagrammatically at 54 and 55. As noted before, during normal operation, the vanes are spread out maximally. The pair of vanes 39, 40 placed on the central shaft in the rearmost position is then the leading pair of vanes, which through catch 55 takes along pair of vanes 37,38. The pair of vanes 37,38 in turn takes along pair of vanes 35,36 through catch 54. As the pair of vanes 35,36 is connected to the central shaft so as to be restrained from rotation relative to it, the central shaft is then caused to rotate. As noted above, in order to prevent damage to the wind turbine at wind forces in excess of normal wind, the vanes can be moved into a position in which they are fully or partially aligned one after the other. For this purpose, vane adjusting means are provided, in the example shown a peg 60, which can turn back the vanes from the maximally spread position, beginning with the leading vane, to decrease the effective number of vanes and hence the wind catching area of the rotor. In the example shown, peg 60 is mounted on a gear 61, placed on the central shaft 30 next to the rearmost rod 34. Gear 61 can in principle rotate freely relative to the central shaft. A relatively small gear 62 meshes with gear 61, and is mounted on a shaft 63 extending through the rods of the vanes. At the front of the packet of vanes, shaft 63 carries a relatively large gear 64, which meshes with a relatively small gear 65 mounted concentrically with the central shaft on the shaft of an electric motor 66. Electric motor 66, that is to say its housing, is fixedly connected to the front, fixed pair of vanes, for example by means of bolts and spacer sleeves, as shown at 67. Accordingly, in operation, the electric motor rotates along with the central shaft. Gears 61,62,64 and 65 and shaft 63 also, in operation, rotate along with the central shaft, but are at rest relative to each other. As soon as, however, the position of the vanes relative to each other needs adjustment, for example, with increasing wind, the electric motor 66 is energized. Gear 65 then rotates relative to the central shaft and drives gear 64, which, in turn, through shaft 63 and gear 62 drives gear 61. Consequently, gear 61 rotates relative to the central shaft. During these movements, peg 60 first takes along the leading vane, and, during continued energization, the next vanes until the wind catching area of the rotor has been sufficiently reduced (or increased). Owing to the selected gear configuration of small gears 62 and 65 and large gears 61 and 64, there is obtained a high-delay transmission, so that the position of peg 60 can be controlled with great accuracy. The electric motor is energized by means of control signals provided by detection means. The detection means are arranged to detect impending overload of the wind turbine and, in response to such detection, to provide control signals. The detection means may, for example, be arranged to detect the speed (rpm) of the central shaft, or any apparatus driven by it, and provide a control signal when a pre-determined threshold value is exceeded. The detection means may also comprise a measuring device which measures the (electric) energy provided by a generator driven by the central shaft, and issue a control signal when a pre-determined threshold value is exceeded. It is noted that, after reading the foregoing, various modifications will readily occur to one skilled in the art. Thus the electric motor 66 may be mounted in a different place, and peg 60 may be actuated in a different manner. To balance the eccentrically rotating mass of gears 62,64 and shaft 63, the fixed rod 32 may, if desired, be provided with a counter weight, as shown diagrammatically at 68. The mass of peg 60 could be balanced, for example, by providing gear 61 with a second peg located radially opposite peg 60. Furthermore, a spring element could be mounted between, for example, the leading vane and the vane coupled with it, which spring element biases the vanes apart to promote the vanes' spreading out from the collapsed position. Thus, for this purpose, in the example of Fig. 4, a spring could be disposed in groove 52, which biases catch 51 towards the end of the groove pointing in the direction of rotation. Also, if desired, the dragger peg may be coupled, either fixedly or resiliently, with the leading vane. The wheel carrying the dragger peg may also be mounted on the central shaft between two rods or even in front of the packet of vanes. These and similar modifications are considered to fall within the scope of the present invention. In the foregoing, it has been described that vanes of a rotor of a wind turbine with a relatively large number of vanes can be turned behind at least one vane which is fixedly connected with the central shaft of the rotor. The drawings show an embodiment employing a pair of vanes fixedly connected to the central shaft of the rotor, and behind which other pairs of vanes can be turned out of the wind. It is also possible to turn the fixed vane or the fixed pair of vanes in front of the freely rotatable (pairs of) vanes. The ultimate effect is the same, namely, that the front vane(s) fully or partially covers or cover the vanes disposed behind the front vane(s) whereby the effective vane area is reduced. It is also possible to use a plurality of fixed pairs of vanes connected to the central shaft of the wind turbine, referred to hereinafter as a fixed ring of vanes, and a plurality of rings of vanes which are adjustable relative to the central shaft, and are arranged, upon impending overload, to be rotated at least partially behind the fixed ring of vanes. As, in such a construction, the effective rotor area is relatively large, even if all adjustable rings of vanes have been moved right behind the ring of vanes fixedly connected to the central shaft (the fixed ring of vanes), the vanes of the fixed ring of vanes may advantageously have a shape which is aerodynamically indifferent, that is to say, such a cross-sectional configuration that wind coming right from afore does not cause the fixed ring to rotate. In this way the speed can be reduced to zero. The vanes of the fixed ring may, for example, have the shape of an isosceles triangle in section, with the apex directed to the front. Such a technique can of course also be used with a wind turbine with only one fixed vane or one fixed vane pair, as shown in Fig. 3. According to a variant of the embodiment with aerodynamically indifferent fixed vane(s) or ring of vanes, the fixed vanes may have an adjustable shape, namely, one which is adjustable between an aerodynamically active and an aerodynamically indifferent shape. Fig. 5 shows schematically in cross-sectional view, an exemplary embodiment of a vane 90 of adjustable shape. The vane shown has a triangular cross-sectional configuration with a base 91, a fixed side 92 and a side 93 which is adjustable in accordance with an arrow 94. Side 93 is hinged at the apex 95 of the triangular shape to the fixed leg 92 or to the body of the vane for hinging movement about an axis extending lengthwise of the vane. The adjustable side can be moved from a rest position shown in solid lines to an active position shown in dash lines at 93'. For operation of the vane, in the example shown, a hinge pin 65 extends up to the vicinity of the rotor shaft, and is connected to the adjustable side so as to be restrained from rotation relative to it. The end of the hinge pin adjacent to the rotor shaft is further provided with an actuating arm 96 extending obliquely downwards by exerting an suitable force on the end of the actuating arm, as indicated by way of example in Fig. 5 with an arrow 97, the adjustable side 93 can be adjusted. The actuation of the adjustable side or of the adjustable sides of a plurality of vanes can be effected, for example, by means of a slidable ring or sleeve mounted around the rotor shaft, and driven by the electric motor 66 as soon as peg 60 has moved all vanes behind the fixed vane(s). For the conversion of the rotary movement of the electric motor into a sliding movement, use can be made, for example, of a helical groove in the shaft of the electric motor and a cam extending into said groove. Fig. 6 shows a diagrammatic front-elevational view of the central section of a plurality of vanes 70-73 which are of variable shape, with pivot pins 74-77 and actuating arms 78-81. An operating ring is shown in dash outline at 82. The vanes which are rotatable relative to rotor shaft 30 are not shown in Fig. 6. It is noted that the actuating arms could be of different shape and that the operating ring, too, could be replaced by a different suitable member. Also, the sides of the triangular cross-sectional shape of the fixed vanes could be of somewhat concavely or convexly curved configuration. When an aerodynamically indifferent vane is used, or a pair or ring of aerodynamically different vanes for covering the other vanes in full or in part in the event of high winds, it is not necessary for the "fixed" vanes to be actually mounted on the rotor shaft so as to be restrained from rotation relative to it. At least one of the other (sets of) vanes, however, should then be mounted on the rotor shaft so as to be restrained from rotation relative to it. A suitable example is a wind turbine with two rings of vanes disposed one behind the other, with the front ring of vanes having vanes with an aerodynamically indifferent shape, or at any rate vanes with an adjustable shape, which can be brought into an aerodynamically indifferent condition, as described hereinbefore. In the case of high winds, the front ring of vanes can then again be turned to cover the rear ring of vanes, either in full or in part. In that configuration, the front ring of vanes may be mounted on the rotor shaft so as to be restrained from rotation relative to it, and the rear rings so as to be freely rotatable on the rotor shaft, or alternatively, the front ring may be freely rotatable and the rear ring restrained from rotation relative to the shaft. The only essential point is that the vanes of the front and rear rings can be rotated relatively to each other into a position in which the vanes are fully or partially aligned with each other. The above and similar modifications will readily occur to one skilled in the art after reading the above.

Claims: A wind turbine of the type having a rotor (1) with a relatively large number of vanes (3-14;35-40; 70-73), characterized in that the vanes are mounted axially behind each other on a central shaft (2;30) of the rotor (1); that at least a number of vanes are mounted for free rotation around the central shaft (2) of the rotor (1) while at least one vane is fixedly connected to the central shaft (2); that the freely rotatable vanes are coupled to adjacent vanes by catch means (51,52); and that detection means are provided for detecting impending overload of the rotor (1), and vane adjusting means (20;60) which in response to such impending overload can rotate said freely rotatable vanes relatively to the central shaft so that said vanes at least partially become axially aligned. A wind turbine as claimed in claim 1, characterized in that said detection means comprise an electrical generator driven directly or indirectly by said central shaft (2;30). A wind turbine as claimed in claim 1 or 2, characterized in that the detection means provide a signal proportional to the speed (rpm) of the central shaft (2;30) of the rotor (1) and that a threshold-value detector is provided arranged to provide an actuating signal to actuate said vane adjusting means (20;60) as soon as the signal from the detection means passes a pre-determined threshold value. A wind turbine as claimed in any one of the preceding claims, characterized in that the vane adjusting means (20;60) comprise an electric motor (66) which, in operation, drives an element (61) that is freely rotatable about said central shaft (2) and is provided with at least one dragger peg (60) capable of rotating the freely rotatable vanes and said at least one fixed vane relatively to each other. A wind turbine as claimed in claim 4, characterized in that the electric motor (66) is mounted coaxially with said central shaft (2) and, in operation, rotates along with said central shaft. A wind turbine as claimed in claim 5, characterized in that the element (61) provided with a dragger peg (60) is a gear, and that said electric motor (66) is coupled with said gear through a first small gear (65) mounted coaxially with said central shaft, a relatively large gear (64) meshing with said first small gear (65), which relatively large gear drives a second small gear (62) through a shaft (63) parallel to said central shaft (2), which second small gear (62) in turn meshes with said gear (61) provided with said peg (60). A wind turbine as claimed in claim 4, 5 or 6, characterized in that said electric motor (66) and said element (61) provided with a dragger peg (60) are disposed on different sides of said vanes. A wind turbine as claimed in any one of the preceding claims, characterized in that a front pair of vanes (35,36) is fixedly connected to said central shaft (2;30) and that the other vanes are rotatable about said central shaft (2;30). A wind turbine as claimed in any one of the preceding claims, characterized in that the vanes are coupled together by means of a catch (51) provided on one vane (50), which engages with a groove (52) of an adjacent vane (53), said catch (51) being capable of moving in said groove (52) between a first position in which the two vanes cover each other, and a second position in which the two vanes make a maximum angle with each other, as viewed in the direction of rotation (p) of the vanes. A wind turbine as claimed in any one of claims 4-9, characterized in that said electric motor (66) is fixedly mounted on said at least one fixed vane (35,36). A wind turbine as claimed in any one of the preceding claims, characterized by spring means provided between at least two vanes and arranged to bias said vanes apart. A wind turbine as claimed in any one of the preceding claims 4-11, characterized in that the dragger peg (21,60) is coupled with a freely rotatable vane. A wind turbine as claimed in any one of the preceding claims, characterized in that the front vane(s) has (have) an aerodynamically indifferent shape to wind blowing on the rotor (1) from afore. A wind turbine as claimed in any one of claims 1-12, characterized in that the front vane(s) has (have) a cross-sectional configuration adjustable between an aerodynamically active form and an aerodynamically indifferent form to wind blowing on the rotor (1) from afore. A wind turbine as claimed in claim 14, characterized in that the front vane(s) of adjustable cross-sectional configuration has (have) a substantially isosceles triangular shape (91,92,93), with the apex (95) of the isosceles triangular shape (91,92,93) being directed to the front and forming a hinge pin extending lengthwise of the vane (90), and relative to which one side (93) of the isosceles triangle can be turned into a position (93') in which it is substantially co-extensive with the other side. A wind turbine as claimed in claim 15, characterized by a hinge pin (74-77) extending along the apex (95) of said at least one vane (70-73;90) of substantially isosceles triangular shape in section, said pin (74-77) being connected to the movable part (94) of the vane so as to be restrained from rotation relative to it, and being provided adjacent to said central shaft with an actuating member (78-81;91). A wind turbine as claimed in claim 16, characterized in that said actuating member (78-81;91) is an arm extending obliquely from said hinge pin (74-77). A wind turbine as claimed in any one of the preceding claims, characterized by a ring of vanes fixedly connected to said central shaft (2;30) and at least one freely rotatable ring of vanes, said rings of vanes being arranged to be rotated relatively to each other. A wind turbine as claimed in claim 18, characterized in that the front ring of vanes has vanes (70-73;90) with an aerodynamically indifferent shape to wind blowing on it from the front. A wind turbine as claimed in claim 18, characterized in that the front ring of vanes has vanes (70-73;90) with a cross-sectional shape which is adjustable between an aerodynamically active form and an aerodynamically indifferent form to wind blowing on the rotor (1) from the front. A wind turbine as claimed in claim 19, characterized in that the cross-sectional configuration of the vanes of the front ring of vanes is a substantially isosceles triangular shape, with the apex (95) of the isosceles triangular shape being directed to the front and forming a hinge pin (74-77) extending lengthwise of the vane, and relative to which one side (93) of the isosceles triangle can be turned into a position (93') in which it is substantially co-extensive with the other side. A wind turbine as claimed in claim 21, characterized in that a hinge pin (74-77) is provided to extend along the apex (95) of a vane of substantially triangular cross-sectional configuration, said pin (74-77) being connected to the movable part (93) of the vane so as to be restrained from rotation relative to it, and having an actuating member (78-81;96) adjacent to said central shaft (2,30). A wind turbine as claimed in claim 22, characterized in that said actuating member (78-81;96) is an arm extending obliquely from said hinge pin (74-77). A wind turbine as claimed in claim 23, characterized by an actuating ring movable lengthwise of the central shaft (2;30) and, in operation, cooperating with the actuating arms (78-81;96) of the vanes having and adjustable shape.

Inventors: BAAS HENDRIK ALBERT, BAAS, HENDRIK ALBERT
Applicants: BAAS HENDRIK ALBERT, BAAS, HENDRIK ALBERT
Application year: 1991
Main classification: F03D7
IPC codes: F03D7